Add discord invite links

Author: dtolnay

_src/help.md

@@ -2,15 +2,18 @@
 
 Serde is one of the most widely used Rust libraries so any place that Rustaceans
 congregate will be able to help you out. For chat, consider trying the
-[#general] or [#beginners] channels of the unofficial community Discord, the
-[#rust-usage] channel of the official Rust Project Discord, or the
-[#general][zulip] stream in Zulip. For asynchronous, consider the [\[rust\] tag
-on StackOverflow][stackoverflow], the [/r/rust] subreddit which has a pinned
-weekly easy questions post, or the Rust [Discourse forum][discourse].
+[#rust-questions] or [#rust-beginners] channels of the unofficial community
+Discord (invite: <https://discord.gg/rust-lang-community>), the [#rust-usage] or
+[#beginners] channels of the official Rust Project Discord (invite:
+<https://discord.gg/rust-lang>), or the [#general][zulip] stream in Zulip. For
+asynchronous, consider the [\[rust\] tag on StackOverflow][stackoverflow], the
+[/r/rust] subreddit which has a pinned weekly easy questions post, or the Rust
+[Discourse forum][discourse].
 
-[#general]: https://discord.com/channels/273534239310479360/274215136414400513
-[#beginners]: https://discord.com/channels/273534239310479360/273541522815713281
+[#rust-questions]: https://discord.com/channels/273534239310479360/274215136414400513
+[#rust-beginners]: https://discord.com/channels/273534239310479360/273541522815713281
 [#rust-usage]: https://discord.com/channels/442252698964721669/443150878111694848
+[#beginners]: https://discord.com/channels/442252698964721669/448238009733742612
 [zulip]: https://rust-lang.zulipchat.com/#narrow/stream/122651-general
 [stackoverflow]: https://stackoverflow.com/questions/tagged/rust
 [/r/rust]: https://www.reddit.com/r/rust