Create index file for docsgen documentation

The current docsgen README file is bloated with information. This ticket will organize the content as follows:

Create an index.md at https://github.com/eosnetworkfoundation/docsgen/tree/main/docs to organize the folder contents.
Move content starting from https://github.com/eosnetworkfoundation/docsgen/blob/main/README.md#initialize-content-repository in the README file and use it as foundation building such an index.md file. Also consolidate https://github.com/eosnetworkfoundation/devrel/blob/1dd83db7ac04ff53404bdba4daf746ab3e4af9ce/Processes/Internal-Build-and-Release-Process.md into that index file.
Make sure all files within the docs folder are accounted for (have an entry in the index file).
Create a "generating content" quick guide on a separate doc file (content currently at https://github.com/eosnetworkfoundation/docsgen/blob/main/README.md#generating-content) and create two paragraphs on index that describe how to generate content using clean_rebuild.sh and generate_documents.sh scripts, respectively.
After moving the content, replace heading Initialize Content Repository with "Documentation" then add a paragraph that links to the index file... "For information on how to generate content, updating site navigation, updating the UX, production setup, and testing, visit the [documentation](index.md) section."

eosnetworkfoundation / devrel