doc: contributing: Tweak the Commit Policy.

Add more examples of when it can be appropriate to push changes without
review, as I think this can be appropriate in the case of trivial changes (as
mentioned before), but also non-trivial fixes.

No longer suggest pushing simple new packages or package upgrades (that don't
cause lots of rebuilds) without sending to guix-patches. Now there's some
automation for testing changes sent to guix-patches, sending changes there
before pushing can mean that more rigorous testing takes place and help speed
up substitutes becoming available. This is true, even if no human review takes
place.

Only suggest waiting one week for review for simpler changes, wait two weeks
for more significant changes.

Also, reorder some of the information in this section so it's grouped together
better.

* doc/contributing.texi (Commit Policy): Tweak.

Signed-off-by: Christopher Baines <mail@cbaines.net>

doc/contributing.texi

@@ -1824,23 +1824,27 @@ It additionally calls @code{make check-channel-news} to be sure
 
 @subsection Commit Policy
 
-If you get commit access, please make sure to follow
-the policy below (discussions of the policy can take place on
+If you get commit access, please make sure to follow the policy below
+(discussions of the policy can take place on
 @email{guix-devel@@gnu.org}).
 
-Non-trivial patches should always be posted to
-@email{guix-patches@@gnu.org} (trivial patches include fixing typos,
-etc.).  This mailing list fills the patch-tracking database
-(@pxref{Tracking Bugs and Patches}).
+Changes should be posted to @email{guix-patches@@gnu.org}.  This mailing
+list fills the patch-tracking database (@pxref{Tracking Bugs and
+Patches}).  It also allows patches to be picked up and tested by the
+quality assurance tooling; the result of that testing eventually shows
+up on the dashboard at
+@indicateurl{https://qa.guix.gnu.org/issue/@var{ISSUE_NUMBER}}, where
+@var{ISSUE_NUMBER} is the number assigned by the issue tracker.  Leave
+time for a review, without committing anything (@pxref{Submitting
+Patches}).  If you didn’t receive any reply after one week (two weeks
+for more significant changes), and if you're confident, it's OK to
+commit.
 
-For patches that just add a new package, and a simple one, it's OK to
-commit, if you're confident (which means you successfully built it in a
-chroot setup, and have done a reasonable copyright and license
-auditing).  Likewise for package upgrades, except upgrades that trigger
-a lot of rebuilds (for example, upgrading GnuTLS or GLib).  We have a
-mailing list for commit notifications (@email{guix-commits@@gnu.org}),
-so people can notice.  Before pushing your changes, make sure to run
-@code{git pull --rebase}.
+As an exception, some changes considered ``trivial'' or ``obvious'' may
+be pushed directly.  This includes changes to fix typos and reverting
+commits that caused immediate problems.  This is subject to being
+adjusted, allowing individuals to commit directly on non-controversial
+changes on parts they’re familiar with.
 
 When pushing a commit on behalf of somebody else, please add a
 @code{Signed-off-by} line at the end of the commit log message---e.g.,
@@ -1855,14 +1859,6 @@ right before pushing:
 make check-channel-news
 @end example
 
-For anything else, please post to @email{guix-patches@@gnu.org} and
-leave time for a review, without committing anything (@pxref{Submitting
-Patches}).  If you didn’t receive any reply after two weeks, and if
-you're confident, it's OK to commit.
-
-That last part is subject to being adjusted, allowing individuals to commit
-directly on non-controversial changes on parts they’re familiar with.
-
 @subsection Addressing Issues
 
 Peer review (@pxref{Submitting Patches}) and tools such as