Add explanation of docs update and ping goals

Co-authored-by: Eric Huss <[email protected]>

Author: Kobzol

src/triagebot/zulip-commands.md

@@ -37,9 +37,8 @@ Note that the impersonation functionality is intended for inspecting the status
 
 - *Meeting* commands serve for controlling the flow of Zulip meetings. They are documented [here](zulip-meeting.md).
 - *Rust Project Goals* commands serve for controlling Rust Project Goal tracking.
-  - `@triagebot ping-goals <threshold> <next-update>`: TODO
-- *Docs update* commands serve for updating documentation
-  - `@triagebot docs-update`: TODO
+  - `@triagebot ping-goals <threshold> <next-update>`: For use by the goals team to ping goal owners on Zulip to give an update on their goal. Will not ping if there has been a comment in `<threshold>` days. `<next-update>` is a string to say when the next blog update will start.
+- `@triagebot docs-update`: Generates a Pull Request ([example](https://github.com/rust-lang/rust/pull/141923)) to update the documentation submodules. See [Documentation Updates](doc-updates.md).
 
 ## Implementation