Add docs for check-in meetings and add diagnostics to the list

Author: oli-obk

about/triage-meeting.md

@@ -19,7 +19,7 @@ This section contains the scheduled check-ins for working groups:
 - **2019-04-18:** [wg-llvm], [wg-async-await],
 - **2019-04-25:** [wg-rfc-2229], [wg-self-profile]
 - **2019-05-02:** [wg-meta], [wg-rls-2.0]
-- **2019-05-09:** [wg-nll]
+- **2019-05-09:** [wg-nll], [wg-diagnostics]
 
 Looking for a meeting that isn't listed above? Make a PR and extend the list to include that
 meeting.
@@ -43,3 +43,4 @@ This section lists check-ins from triage meetings before the check-in schedule w
 [wg-pgo]: ../working-groups/pgo
 [wg-mir-opt]: ../working-groups/mir-opt
 [wg-pipelining]: ../working-groups/pipelining
+[wg-diagnostics]: ../working-groups/diagnostics

procedures/form-new-working-group.md

@@ -103,9 +103,11 @@ The basic steps to setup a working group are as follows:
   listed and a link to their directory in this repository should also be included. See the
   traits working group [as an example][team_repo_example]. This will ensure that the working groups
   are listed on the website.
+- Add a check-in for your working group to the [compiler-team meeting check-in list](check_in)
 
 [team_repo]: https://github.com/rust-lang/team
 [team_repo_example]: https://github.com/rust-lang/team/blob/master/teams/wg-traits.toml
 
+[check_in]: ../about/triage-meeting.md
 [README]: ../README.md
 [template]: ../working-groups/.template