diff ESC documentation

[Dan Jacobson]

Clarify here if you mean ESC or ESC and C-c

      Diff mode:
      Major mode for viewing/editing context diffs.
      ...
===>  When the buffer is read-only, the ESC prefix is not necessary.
      ...
      You can also switch between context diff and unified diff with
      C-c C-u, or vice versa with C-c C-d and you can also reverse the
      direction of a diff with C-c C-r.
      key             binding
      ---             -------
===>  C-c               Prefix Command
===>  ESC               Prefix Command

      C-c C-a           diff-apply-hunk
      C-c C-c           diff-goto-source
      C-c C-d           diff-unified->context
      C-c C-e           diff-ediff-patch
      C-c C-f           next-error-follow-minor-mode

Also add/mention the command to "rerun the diff" / "run the diff again".