Updated anaconda install instructions (#617)

    <ol>

      <li>Download either the Anaconda or Miniconda installation script for your OS platform.  Anaconda is a much larger distribtion of packages supporting scientific python, while Miniconda is a minimal installation and not as large:

      <a href="https://www.anaconda.com/download">Anaconda installer</a>, <a href="https://conda.io/miniconda.html">Miniconda installer</a></li>

      <li>If you are running on some variant of Linux, open a terminal window in the directory where you downloaded the script, and run the following commands.  In this example, we chose to do a full install of Anaconda, and our OS is Linux-based.  Your file name may be different depending on your environment.</li>

      <li>If you are running on some variant of Linux, open a terminal window in the directory where you downloaded the script, and run the following commands.  In this example, we chose to do a full install of Anaconda, and our OS is Linux-based.  Your file name may be different depending on your environment.

        <pre>

          <strong>chmod +x Anaconda3-5.2.0-Linux-x86_64.sh</strong>

          <strong>./Anaconda3-5.2.0-Linux-x86_64.sh</strong>

        </pre>

        This will start the Anaconda installer which will guide you through the installation process.

      <li>After the installation has finished, open up a bash prompt in your terminal window.</li>

        This will start the Anaconda installer which will guide you through the installation process.</li>

      <li>If you are running Mac OS X, a pkg file (which looks similar to Anaconda3-5.3.0-MacOSX-x86_64.pkg) will be downloaded.  Double-click on the file to start the installation process.</li>

      <li>Again from within a terminal window, create a new environment for your ISIS3 installation:

      <li>After the installation has finished, open up a bash prompt in your terminal window.</li>

      <li>Next setup your Anaconda environment for ISIS3. In the bash prompt, run the following commands:

        <pre>

          <em>#Add the following channels to the Anaconda installation</em>

          <strong>conda config --add channels conda-forge</strong>

          <strong>conda config --add channels usgs-astrogeology</strong>

          <em>#Create a new conda environment to install ISIS3 in</em>

          <strong>conda create -n isis3 python=3.6</strong>

          <em>#Activate the environment</em>

          <em>#Depending on your OS, you may need to use conda activate isis3 instead</em>

          <strong>source activate isis3</strong>

          <em>#Add the following channels to the environment</em>

          <strong>conda config --env --add channels conda-forge</strong>

          <strong>conda config --env --add channels usgs-astrogeology</strong>

          #Verify you have the correct channels:

          <strong>conda config --show channels</strong>

          <em>#The order is important.  If conda-forge is before usgs-astrogeology, you will need to run:</em>

           <strong>conda config --add channels usgs-astrogeology</strong>

          <strong>conda config --env --add channels usgs-astrogeology</strong>

        </pre></li>

          <em>#Create a new conda environment to install ISIS3 in.</em>

          <strong>conda create -n isis3</strong>

          <em>#Activate the environment</em>

          <strong>source activate isis3</strong>

          <em>#Download the ISIS3 version</em>

      <li>The environment is now ready to download ISIS3 and its dependencies:

        <pre>

          <strong>conda install -c usgs-astrogeology isis3</strong>

        </pre></li>

      <li>Finally, setup the environment variables:

        <pre>

          <em>#Execute the ISIS3 variable initialization script with default arguments.</em>

          <em>#This script prepares default values for:  $ISISROOT/$ISIS3DATA/$ISIS3TESTDATA</em>

          <strong>python $CONDA_PREFIX/scripts/isis3VarInit.py</strong>

        </pre>

        Executing this script with no arguments will result in $ISIS3DATA=$CONDA_PREFIX/data,

        and $ISIS3TESTDATA=$CONDA_PREFIX/testdata.  The user can specify different directories

        for both of these optional values:

         <strong>./$CONDA_PREFIX/scripts/isis3VarInit --data-dir=[path to data directory]  --test-dir=[path to test data directory]</strong>

        <pre>

          <strong>python $CONDA_PREFIX/scripts/isis3VarInit.py --data-dir=[path to data directory]  --test-dir=[path to test data directory]</strong>

        </pre>

        Directions for running rsync to download ISIS3 data can be found <a href="#ISIS3DataDownload">here.</a>

          <em>#Run the source activate command a second time to process the changes:</em>

          <strong>source activate isis3</strong>

          To avoid having to do this every time you open a new terminal window, we suggest adding the following lines to the end of your .bashrc file 

          (if running a variant of Linux) to ensure that conda is in your PATH variable.  If you are running Mac OS X, these lines would be appended

          to the end of your .bash_profile file:

          <strong>source activate isis3</strong>

          <strong>python $CONDA_PREFIX/scripts/isis3VarInit.py</strong>

        Now everytime the isis3 environment is activated, $ISISROOT, $ISIS3DATA, and $ISIS3TESTDATA

        will be set to the values passed to isis3VarInit.py. This does not happen retroactively,

        re-activate the isis3 envionment with the following command:

        <pre>

          <em>#Depending on your OS, you may need to use conda activate isis3 instead</em>

          <strong>source activate isis3</strong>

        </pre></li>

    </ol>

        </pre>

      </li>

    </ol>

  <h3>Operating System Requirements</h3>

  <p>ISIS3 runs on many UNIX variants. ISIS does not run natively on MS Windows,

     although it has been successfully run on Windows 10 using the Windows

      <li>Ubuntu 18.04 LTS</li>

      <li>Mac OS X 10.13.6 High Sierra</li>

      <li>Fedora 28</li>

      <li>CentOS 7.2</li>

    </ul>

<p>

    ISIS3 may be run on other Linux or macOS operating systems then those listed above,

    but it has not been tested and is not supported.

</p>

   <h3>Hardware Requirements</h3>

   <p>Here are the minimum hardware requirements</p>

    <ul>