Apologies if this is obvious to all, but I figured I'd share as it took a moment to look it up and get the right answer out of the noise on StackOverflow :)
A simple way to apply a GitHub pull request, say:
https://github.com/apache/commons-lang/pull/11/
Download (wget etc) https://github.com/apache/commons-lang/pull/11.patchand use:
patch -p1 < 11.patch
[huge assumption that people have patch on the command line]
Hen
