GitHub doesn't capitalize things like pull request, fork, push...neither should you. E.g. "Pull requests let you tell others about changes you've pushed to a repository on GitHub. Once a pull request is sent, interested parties can review the set of changes, discuss potential modifications, and even push follow-up commits if necessary."
However, when you refer to the name of a feature or page, then use caps. E.g. "You can view and sort long-running pull requests from your repository's Pull Request page."
GitHub doesn't capitalize things like pull request, fork, push...neither should you. E.g. "Pull requests let you tell others about changes you've pushed to a repository on GitHub. Once a pull request is sent, interested parties can review the set of changes, discuss potential modifications, and even push follow-up commits if necessary."
However, when you refer to the name of a feature or page, then use caps. E.g. "You can view and sort long-running pull requests from your repository's Pull Request page."
When in doubt, check their docs.