Improve room directory content

[nadonomy]

With the changes being made to home & welcome, we should improve the content of the room directory to aid discoverability.

[ara4n]

the content side of this is mitigated to some extent by matrix-org/synapse#4647 (and deployed on matrix.org to remove some of the more insalubrious rooms from the published list)

[nadonomy]

@lampholder did you add needs-design to this issue erroneously or am I missing some context? This issue was meant to only address the content that populates the room dir.

[lampholder]

Yep, looks like I misapplied the label, sorry.

[jryans]

Is this done then, with the Synapse-side mitigations? Or is there more we plan to do here?

[nadonomy]

Yep, I believe done. Considering there's no riot work, and the synapse updates are deployed I'll close.