SCRIPTS: announce-release: add the link to the wiki in the announce messages

Let's add the link to the wiki to the announce messages, plenty of
users don't even know it exists.
diff --git a/scripts/announce-release b/scripts/announce-release
index 0c1f607..88274a0 100755
--- a/scripts/announce-release
+++ b/scripts/announce-release
@@ -165,6 +165,7 @@
  echo "   Discourse        : http://discourse.haproxy.org/"
  echo "   Slack channel    : https://slack.haproxy.org/"
  echo "   Issue tracker    : https://github.com/haproxy/haproxy/issues"
+ echo "   Wiki             : https://github.com/haproxy/wiki/wiki"
  echo "   Sources          : http://www.haproxy.org/download/${BRANCH}/src/"
  echo "   Git repository   : http://git.haproxy.org/git/${gitdir}/"
  echo "   Git Web browsing : http://git.haproxy.org/?p=${gitdir}"