Add examples to patch's help

[plumenator]

Close #3030

[ceedubs]

Thanks a lot for the PR, @plumenator!

I think that there should be an example for the no-arg version that uses the default patch in the current namespace.

It's news to me that you can also pass in a namespace. That's a thing @aryairani? If so, should the example not have the square braces in [path] since this is the example where path is being provided and there's another example where it's not?

[plumenator]

The patch arg is required. As for the path example, I followed the todo example:

unison/unison-cli/src/Unison/CommandLine/InputPatterns.hs

Line 133 in 0a0e089

( makeExample todo ["<patch>", "[path]"],

[ceedubs]

@plumenator sorry I think that I was confused both in my comment on this PR and in the original issue that I created. Thanks for setting me straight and for fixing the docs!