Clarify that T-compiler meetings are text-mode only

[apiraino]

From comment: #865 (comment)

The fact that the compiler meetings are purely textual (i.e. without voice / video chat) was strange enough to me that I kept looking for a Google Meet link, even though the docs stated fairly clearly that meetings happen on Zulip.

Rendered

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[madsmtm]

Thanks, "text-mode only" was the words I was looking for, and the rewording generally makes sense to me.