Generate correct links to repo

On [React native paper doc website](https://callstack-io.github.io/react-native-paper/getting-started.html), `default theme` link has wrong path. Instead of pointing link back to the website, we should point it to the repo files.

Open the React Native Paper documentation page at getting-started.html and inspect the `default theme` link. Trace it to the corresponding documentation source and update the destination so it points to the repository files rather than back to the website; verify the generated link on the documentation page.

索引モデルが issue の本文から書いたものです。