It was noticed that, ~70% of users were accessing the project's IRC
channel via the Matrix.org "portal" room.

Matrix provides some additional useful features (e.g. read receipts,
message reactions, more flexible moderation, and Rust syntax
highlighting in the reference Matrix client), so the project has
registered `#zbus:matrix.org` to give the project full control of their
Matrix room (to ease future room management etc.).

Link to the new Matrix room in the docs, using the `matrix.to` canonical
URL, to permit low-friction access to the Matrix room. This makes the
more featureful, and beginner-friendly "Matrix direct" option the
default (retaining a reference to the bridged Freenode IRC channel for
those that prefer it).