adding from source install instructions

INSTALLATION.md

@@ -26,3 +26,41 @@ Xarray, Scikit-learn, etc. when creating an environment.
 If you are interested in learning more about how Conda environments work, please visit
 the [managing environments](https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html)
 page of the Conda documentation.
+
+
+## Building GeoCAT-viz from source
+
+Building GeoCAT-viz from source code is a fairly straightforward task, but
+doing so should not be necessary for most users. If you are interested in
+building GeoCAT-viz from source, you will need the following packages to be
+installed.
+
+### Required dependencies for building and testing GeoCAT-viz
+
+- Python 3.6+
+- [GeoCAT-datafiles](https://github.com/NCAR/geocat-datafiles)  (For tests only)
+- [netcdf4](https://unidata.github.io/netcdf4-python/)  (For tests only)
+- [numpy](https://numpy.org/doc/stable/)
+- [xarray](http://xarray.pydata.org/en/stable/)
+- [matplotlib](https://matplotlib.org/stable/)
+- [cartopy](https://scitools.org.uk/cartopy/docs/latest/)
+
+
+### How to create a Conda environment for building GeoCAT-viz
+
+The GeoCAT-viz source code includes a conda environment definition file,
+`conda_environment.yml` in the root directory that can be used to create a
+development environment containing all of the packages required to build GeoCAT-viz.
+
+    conda env create -f conda_environment.yml
+    conda activate geocat-viz
+
+### Installing GeoCAT-viz
+
+Once the dependencies listed above are installed, you can install GeoCAT-viz
+with running the following command from the root-directory:
+
+    pip install .
+
+For compatibility purposes, we strongly recommend using Conda to
+configure your build environment as described above.

conda_environment.yml

@@ -13,5 +13,6 @@ dependencies:
   - scikit-learn
   - sphinx
   - wrf-python
+  - pip
   - pip:
       - pre-commit