docs: projects.md to include type information

[atomicpages]

Summary:

While upgrading from 0.67 to 0.7x finding react-native.config type information was not obvious. Adding annotations so autocomplete works on most editors.

Test Plan:

Just docs

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md

[szymonrybczak]

Thanks! That's nice improvement, maybe we could do it everywhere in our docs, I see that there are other places :D