misc: Updated CONTRIBUTING.md to discuss WIP changes

Previously CONTRIBUTING.md discused private changes, but contributors
cannot submit private changes to Gerrit under the current configuration.
This has therefore been removed and replaced with an explanation of how
to submit a WIP (Work In Progress) changes to Gerrit. WIP changes are

Change-Id: I9e1acbdaf4a9b5c433c0704ba9faf325a6b48c6a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24805
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
index 7b3dcfd..2a24f05 100644
@@ -276,20 +276,35 @@
  git commit --amend
-Push change to gerrit as a draft/private
+Push change to gerrit as a Work In Progress
-See https://gerrit-review.googlesource.com/Documentation/intro-user.html#private-changes
-for details on private gerrit changes.
+It is acceptable to push commits as "Work In Progress" (WIP) changes within
+gerrit. WIP changes are publicly visible though no one will be able to review
+the changes or be directly notified they have been submitted. WIP changes can
+be useful for backing up code currently under-development or for sharing
+incomplete code with the wider community (i.e., the link to the gerrit change
+may be shared, and others may download the change, comment on it, and track
+alterations over time).
+See https://gerrit-review.googlesource.com/Documentation/intro-user.html#wip
+for details on WIP gerrit changes.
+To push a change as a WIP:
- git push origin HEAD:refs/for/develop%private
+ git push origin HEAD:refs/for/develop%wip
-Once you have pushed your change as "private", you can log onto [gerrit]
-(https://gem5-review.googlesource.com) and once you're happy with the commit
-click the "unmark private" which may be hidden in the "more options" dropdown
-in the upper right corner.
+Once you have pushed your change as a WIP, you can log onto [gerrit](
+https://gem5-review.googlesource.com) and view it. Once you're happy with the
+change you can add reviewers which shall move your change from WIP status
+to be considered for submission by the wider gem5 community. Switching from a
+WIP to a regular change does not notify the gem5 community, via the gem5-dev
+mailing-list, that a change has been submitted (as would occur if a change were
+submitted directly for review). It is therefore important to include reviewers
+and CC those who you wish to view the change (they will be notified
+automatically via email).
 Push change bypassing gerrit