Summary:
Several changes here. The `Text.md` and `PixelRatio.md` files were appended to the autodocs during site generation. This seemed excessive for just two files, so I've just merged the content into the autodocs themselves. It should help us simplify the website generation process in the future.
I've also merged IssueGuidelines.md and PullRequestGuidelines.md into the Contribution/Maintainers guidelines to improve their visibility.
Finally, I renamed Help to Community in the nav bar.
Ran the website locally, and verified every page rendered as expected: the Community page, Contributing page, Maintainers page.
Closes https://github.com/facebook/react-native/pull/15374
Differential Revision: D5567400
Pulled By: hramos
fbshipit-source-id: e06056edb12c9a17319fe1af46b2ef3a2e1b5854
5be8c4af26