doc: update commit-queue documentation

update the commit-queue contributing documentation by:
 - removing the references of the feature being experimental
 - clarifying that it applies on mergeable pull requests

Author: dario-piotrowicz

doc/contributing/commit-queue.md

@@ -1,10 +1,8 @@
 # Commit queue
 
-> Stability: 1 - Experimental
-
 _tl;dr: You can land pull requests by adding the `commit-queue` label to it._
 
-Commit Queue is an experimental feature for the project which simplifies the
+Commit Queue is a feature for the project which simplifies the
 landing process by automating it via GitHub Actions. With it, collaborators can
 land pull requests by adding the `commit-queue` label to a PR. All
 checks will run via `@node-core/utils`, and if the pull request is ready to
@@ -18,7 +16,7 @@ implementation details, reasoning for design choices, and current limitations.
 From a high-level, the Commit Queue works as follow:
 
 1. Collaborators will add `commit-queue` label to pull requests ready to land
-2. Every five minutes the queue will do the following for each pull request
+2. Every five minutes the queue will do the following for each mergeable[^1] pull request
    with the label:
    1. Check if the PR also has a `request-ci` label (if it has, skip this PR
       since it's pending a CI run)
@@ -122,3 +120,7 @@ once we start using the Commit Queue we notice that the number of required
 reverts increases drastically, we can pause the queue until a Revert Queue is
 implemented, but until then we can enable the Commit Queue and then work on a
 Revert Queue as a follow-up.
+
+[^1]: A PR is considered mergeable when it's been open for at least two days (unless
+    it's being fast-tracked) and has more than one collaborator's approval or if it's
+    been open for at least seven days and has at least one collaborator's approval.