Add the -a param to the docs

[est31]

The patch utility does not understand git formatted patches.
For text files, there is no problem, but binary files use a format patch doesn't understand.

The -a param makes git diff put binary files into the patch in
raw format that can be understood by the patch tool.

[est31]

@ryantm friendly ping

[ryantm]

I don't feel particularly qualified to review this. Is it really the case that we want to have patches of binary files in nixpkgs? It seems like it would be really hard to review that the patch is doing the right thing. Why not build from source and use a source patch?

[est31]

shared-mime-info contains binary files as part of the test suite. Before updating it altogether in #126050 I first tried backporting the PR I wanted. That PR also altered the test suite so it added binary files. I wondered for hours how I could get the patch file into a format that nix would accept, as it didn't like git formatted patches until I discovered the -a option. git supports this out of the box so I feel that the recommended command from the docs supporting binary files out of the box would be good as well.

[ryantm]

Okay, I don't think this will actually actively encourage people to actually merge binary patches to nixpkgs, and it sounds like it might have saved some time in your case, so sure, let's merge it.