Document which Gerrit versions are actively maintained

The Gerrit open source community only supports the last 2 versions
actively but so far this wasn't documented. Add this information to the
homepage and make clear that all support happens on a best effort basis
as Gerrit is an open source project and we do not offer support
contracts.

Also mention that the repo-discuss mailing list is managed and new posts
need to be approved before they appear on the mailing list. This may
help to avoid duplicate posts from new participants.

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: Idb7a3c39da0a96c605fd0c4219cc195e7b64ab8a
diff --git a/index.md b/index.md
index 66441a6..3109749 100644
--- a/index.md
+++ b/index.md
@@ -126,11 +126,26 @@
 
 ## Support
 
-Write to the mailing list (<a href="https://groups.google.com/group/repo-discuss">repo-discuss on Google Groups</a>),
+The Gerrit open source community actively supports the last 2 releases
+on a best effort basis. Older releases are not actively maintained but
+may still receive important fixes (e.g. security fixes), but there is
+no guarantee for this. Which fixes are backported to these old
+releases is decided on a case by case basis.
+
+End of life for old releases is not announced but happens implicitly
+when a new Gerrit version is released.
+
+For questions write to the mailing list (<a href="https://groups.google.com/group/repo-discuss">repo-discuss on Google Groups</a>),
 join the IRC channel <a href="https://echelog.com/logs/browse/gerrit/">#gerrit</a>, or
 check the questions tagged with <a href="https://stackoverflow.com/questions/tagged/gerrit">[gerrit]</a>
 on Stack Overflow.
 
+The repo-discuss mailing is managed to prevent spam posts. This means
+posts from new participants must be approved manually before they
+appear on the mailing list. Approvals normally happen within 1 work
+day. Posts of people that participate in mailing list discussions
+frequently are approved automatically.
+
 ## Social Media
 
 Follow us on Twitter (<a href="https://twitter.com/gerritreview">@gerritreview</a>) and