Add docs for open- and browse-wiki Emacs functions.

Hey Jeremy, I have recently written some small helper functions to supplement tid-mode, and thought I would update the docs to reflect that.

I realize this is a slightly bigger docs change than I've made in the past. Let me know if the docs' style or formatting is incorrect, or if you'd like some more information. Also, I wouldn't be surprised if I had some more commits in the near future to update, extend, or adjust this.