update readme with zulip stream

Author: syphar

README.md

@@ -257,4 +257,4 @@ When updating Font Awesome, make sure to change `$fa-font-path` in `scss/_variab
 ### Contact
 
 Docs.rs is run and maintained by the [docs.rs team](https://www.rust-lang.org/governance/teams/dev-tools#docs-rs).
-You can find us in #docs-rs on [Discord](https://discord.gg/f7mTXPW).
+You can find us in #t-docs-rs on [zulip](https://rust-lang.zulipchat.com/#narrow/stream/t-docs-rs)