Doc: commit access follows demonstrated judgement, not a single clean PR

CONTRIBUTING.rst

@@ -468,15 +468,18 @@ If in doubt, go ahead and open a PR with your best guess and we can discuss this
 Joining the Development Team
 ----------------------------
 
-Anyone who has successfully seen through a pull request which did not
-require any extra work from the development team to merge will
-themselves gain commit access if they so wish (if we forget to ask please send a friendly
-reminder).  This does not mean there is any change in your contribution workflow:
-everyone goes through the same pull-request-and-review process and
-no-one merges their own pull requests unless already approved.  It does however mean you can
-participate in the development process more fully since you can merge
-pull requests from other contributors yourself after having reviewed
-them.
+Commit access is an invitation the development team extends once a contributor
+has shown a developed sense for the project -- its scope, its conventions, and
+what a change costs the people who depend on it.  We look for that across
+contributions, reviews and discussions rather than in any single pull request,
+so there is nothing to clear on demand; if we haven't reached out yet, that is
+not a verdict on your work -- sometimes no-one has thought to offer.
+
+The invitation does not change how you contribute: everyone goes through the
+same pull-request-and-review process, and no-one merges their own pull requests
+unless already approved.  It does mean you can take a fuller part in the
+development process, since you can merge other contributors' pull requests once
+you have reviewed them.
 
 
 Merge/squash guidelines