doc: add author-ready label ref to onboarding-extras guide
The "Labels" section of doc/guides/onboarding-extras.md
was missing a reference to the author-ready
label. This commit adds a description similar to the definition found in doc/guides/collaborator-guide.md
with the goal of making it easier for new contributors to find labels info all in one place.
Just a small improvement suggested during the onboarding session
/cc @addaleax
Checklist
-
make lint
passes -
documentation is changed or added -
commit message follows commit guidelines