Previously our automatic React injection approach injected `import React from 'react'` automatically whenever JSX was detected. The new official JSX transform solves this by enforcing importing `React` when it is used.
This codemod automatically converted files that are using a "global React variable" to use `import React from 'react'`
- Updated some links in docs that don't have the `.md` extension. Not required for our live docs but useful for the GitHub view.
- Updated links that go to https://nextjs.org/docs to a relative path, that way they'll work for versioned docs
- Updated the `Regex Path Matching` example to be consistent with the paragraph above and with the official example in /examples.