AAH and also Galaxy are automatically trying to render the base README.md
file in the collection even if "readme" is set to another file in galaxy.yml.
Fixes:
1) README.md is renamed to README-COLLECTION.md
2) New README.md is generated with information about the rename and also
pointing to the README-COLLECTION.md file in the collection and also
the upstream documentation (versioned and latest).
3) Upstream "documentation" in galaxy.yml set to new README.md file.