Update repository references for linkifiers in Zulip

[firefighterduck]

The current document about the rust-lang Zulipchat contains not-up-to-date information about the usage of linkifiers. For one thing, the repositories of Chalk, Ena and Polonius are referenced under their old rust-lang-nursery names. This should be updated to reference the new rust-lang repositories.

It might also be noteworthy that there exist a few other linkifiers that might be relevant to have in this document, e.g. foundation#2334 for rust-lang/rust-founadation-exploration (whenever this will be an actual thing, the linkifier is already set up) or cargo#3434 for rust-lang/cargo. I would suggest to either have an exhaustive list of all linkifiers or link directly to the corresponding settings page as well as add the most important ones (whichever that may be).

[ehuss]

I'm going to close as I think this is effectively resolved by #700 (and #477).