Add patch command.

Add tldr docs for the patch command.
Just to make sure I understand what's going on with that command: it does **apply the reverse of a patch**, right? If so, *that's* what's happening, not the patch (file) itself being reversed -- which is the interpretation I make of "reverse a patch", hence my confusion.

In another words: if the command indeed operates not on the patch, but on the files *indicated by the patch*, then the verb (apply, reverse, etc) should always refer to what will happen to the files mentioned in the patch, in order to maintain consistency.