Add projection web app documentation

The website will have general instructions for use. This page will have formatting instructions, details about how data is calculated and exported, etc.

Replaces:
https://github.com/blekhmanlab/compendium_docs/blob/1.2.0/docs/source/projectionist/index.rst
https://github.com/blekhmanlab/compendium_docs/blob/1.2.0/docs/source/projectionist/reference.rst

Start by reading the replaced docs/source/projectionist/index.rst and docs/source/projectionist/reference.rst files linked in the issue, then inspect the current web app documentation structure. Done means a replacement page covers general use, formatting, data calculation, and export instructions.

Written by the indexing model from the issue text.