Uplift Gratibot docs and add diagrams

[gesparza3]

Utilize Backstage to expand on Gratibot setup instructions, how it works, and how to contribute to the app

[chodges7]

Right now, the README.md in root is a concatenated version of the docs in the docs folder. GitHub can see a README.md file in the docs folder so we should separate out and add links to different markdown files in the main readme and move it to the docs folder.

[chodges7]

mkdocs.yml is how one would edit how the docs appear in Backstage.

Note: need to be on the internal VPN to access Backstage