Create codefmt usage screencast for README.md

[dbarnett]

Lots of vim plugins have fancy screencasts (animated GIFs) in the README.md showcasing plugin features. The codefmt plugin has several useful features that would make a nice screencast.

We should create a screencast and embed it in our README.md. If we could also include a keyboard monitor in the screencast, that would help show off all the handy mappings.

[rnmhdn]

Actually I can't even find what the mappings are!
I could find it from :h FormatCode yet I think it would have been better if you have listed some of the useful mappings in the readme.md

[dbarnett]

They're mentioned in the helpfile (specifically :help codefmt-mappings). Any clarifications you're looking for there?

[rnmhdn]

No. I just thought it would have been better if you put a few of them in the readme.md here.