Explain how SRV works in Matrix and discourage using it (#2577)
Explain how SRV works in Matrix and discourage using it (#2577)

* Explain how SRV works in Matrix and discourage using it

* Minor tweaks to formatting

Co-authored-by: Neil Alexander <7f0e7998f0d3082a84355a2366a12924c14a9eda@users.noreply.github.com>
matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite