Add explanations for undocumented labels
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 6d150c0..741ced8 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -403,9 +403,15 @@
* Dark blue, **beta-** labels track changes which need to be backported into
the beta branches.
+* Light purple, **C**-prefixed labels represent the **category** of an issue.
+
* Green, **E**-prefixed labels explain the level of **experience** necessary
to fix the issue.
+* The dark blue **final-comment-period** label marks bugs that are using the
+ RFC signoff functionality of [rfcbot][rfcbot] and are currenty in the final
+ comment period.
+
* Red, **I**-prefixed labels indicate the **importance** of the issue. The
[I-nominated][inom] label indicates that an issue has been nominated for
prioritizing at the next triage meeting.
@@ -413,10 +419,26 @@
* The purple **metabug** label marks lists of bugs collected by other
categories.
+* Purple gray, **O**-prefixed labels are the **operating system** or platform
+ that this issue is specific to.
+
* Orange, **P**-prefixed labels indicate a bug's **priority**. These labels
are only assigned during triage meetings, and replace the [I-nominated][inom]
label.
+* The gray **proposed-final-comment-period** label marks bugs that are using
+ the RFC signoff functionality of [rfcbot][rfcbot] and are currently awaiting
+ signoff of all team members in order to enter the final comment period.
+
+* Pink, **regression**-prefixed labels track regressions from stable to the
+ release channels.
+
+* The light orange **relnotes** label marks issues that should be documented in
+ the release notes of the next release.
+
+* Gray, **S**-prefixed labels are used for tracking the **status** of pull
+ requests.
+
* Blue, **T**-prefixed bugs denote which **team** the issue belongs to.
If you're looking for somewhere to start, check out the [E-easy][eeasy] tag.
@@ -424,6 +446,7 @@
[inom]: https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3AI-nominated
[eeasy]: https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3AE-easy
[lru]: https://github.com/rust-lang/rust/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-asc
+[rfcbot]: https://github.com/dikaiosune/rust-dashboard/blob/master/RFCBOT.md
## Out-of-tree Contributions
