Fix typo

README.md

@@ -111,7 +111,7 @@ To contribute to Rust, please see [CONTRIBUTING.md](CONTRIBUTING.md).
 Rust has an [IRC] culture and most real-time collaboration happens in a
 variety of channels on Mozilla's IRC network, irc.mozilla.org. The
 most popular channel is [#rust], a venue for general discussion about
-Rust, and a good place to ask for help,
+Rust, and a good place to ask for help.
 
 [IRC]: https://en.wikipedia.org/wiki/Internet_Relay_Chat
 [#rust]: irc://irc.mozilla.org/rust