document finally in try/catch

[stevengj]

As noted on discourse, the try docstring should at least briefly mention finally.

[Seelengrab]

LGTM

[jariji]

This PR copies from the finally docstring. In both places it shows how to combine try with finally but not how to combine try/catch with finally. Eg if you've never seen finally before, you might wonder is it try/finally/catch or try/catch/finally or what. Suggested fix: include a try/catch/finally example.

[stevengj]

I added a catch block to the example.