Installation instructions

[ahuang11]

Maybe add a short blurb on how to install and test the development version:

This worked for me.

git clone https://github.com/jthielen/OpenMosaic.git
cd OpenMosaic
conda install -c conda-forge gdal
pip install -e .

[jthielen]

Thanks for the recommendation! I think I'll create a recommended environment.yml to install the needed packages in place of the conda install ... line, but other than that, your suggested blurb looks great.