Patching Packages

• Common scenario where a pull request hasn't been merged or a new release hasn't been cut, but a change should be applied to a given package.

• Cover patches attr for mkDerivation

• Introduce fetchpatch utility

  • Show example
  • Make note that fetchpatch does it's own sanitization, meaning that fetchpatch and nix-prefetch-url will generally create different FODs
  • Make note that generally a comment should be added to explain why a patch is being added, and when is it an appropriate time to remove it