Refined-github: Warn when creating a PR from master branch

[sindresorhus]

Creating a PR from master branch is an anti-pattern, but I still see many users that do it. This creates many problems, like accidentally committing to an older open PR by just committing to their fork's master branch. Would be nice to show a big warning with a link to an explanation why they should create a PR-specific branch instead if they try to create a PR from master.

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_For anyone that wants this, please also send this feature request to GitHub: [email protected]_

[fregante]

This shouldn't be too hard.

The URL looks like this:

https://github.com/babel/babel/compare/master...bfred-it:master

If feature.isCompare and if location.pathname ends in `${getUsername()}:${getDefaultBranch()}`, add warning somewhere on the page.

PR welcome

[alejandro-angulo]

Created a PR for this here: https://github.com/sindresorhus/refined-github/pull/1758 .