cheat-sheet.md: Mention 'config', 'diff', 'branch', 'remote', ...

cheat-sheet.md: Mention 'config', 'diff', 'branch', 'remote', ...

Also mention:

* checkout
* rebase
* commit --amend
* reset

With the exception of 'commit --amend', these were all used or
mentioned in Matt Davis' Git-via-GitHub notes [1].

After editing cheat-sheet.md in my text editor, staging and committing
it was the usual:

  $ git add cheat-sheet.md
  $ git commit --all --verbose

[1]: http://git.tremily.us/?p=swc-version-control-git.git;a=commit;h=fda4a1a751211ccbf9deac1d5bea7d7f1ad0f033