message: add help email mention to the policies page
diff: In general, these policies are guidelines. Problems are often contextual, and
  exceptional circumstances sometimes require exceptional measures. We plan to
  continue to clarify and expand these rules over time as new circumstances
  -arise.
  +arise. If your problem is not described below, consider [sending us an email].
  # Package Ownership
  @@ -50,3 +50,4 @@ of Conduct may be removed. There are two important, related aspects:
  must be taken into consideration in these kinds of situations.
  [Code of Conduct]: https://www.rust-lang.org/conduct.html
  +[sending us an email]: mailto:help@crates.io
  