Add a watch mode and bell on push/pull needed.

Adds the following options:
- --watch: makes it clear the screen, display the status info,
  and then wait for a configurable amount of time (default 30s)
  before displaying again.
- --seconds: configures the amount of time to sleep.
- --bell: if a branch needs pushing or pulling, send a bell to
  the terminal.
Fix copy/paste error preventing correct remote fetch.
Combine watch and seconds args into one.
Add new args to the README.
Merge pull request #2 from stormbrew/watch-mode

Add a watch mode and bell on push/pull needed.