Put a banner at the top of the mq page recommending bookmarks

[kewisch]

https://developer.thunderbird.net/contributing/fixing-a-bug/using-mercurial-queues describes using mq. For various reasons the current recommendation is to use bookmarks, so for people who don't know either I think we should be recommending bookmarks. I think we should:

• Make bookmarks the first link in that section
• Put a banner on the mq page saying that developers should prefer bookmarks.

[kewisch]

https://www.mercurial-scm.org/wiki/MqExtension#A_word_of_warning_for_new_users

[Alecaddd]

Yes, that's a really good point. Thanks for opening this issue. I agree with both actions you recommended.

If you want, I can take care of this later today, if you don't already have a PR for it. Cheers.