Provide link in case redirect fails

[niconii]

Browsers using uMatrix or uBlock to block JavaScript appear to block <noscript> tags as well.

gorhill/uMatrix#319
gorhill/uBlock#308

In other words, neither <script> nor <noscript> can be relied on to work. This PR adds a body to the redirect page which provides a link, in case the redirect fails.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[alexcrichton]

Thanks!