SCRIPTS: add the issue tracker URL to the announce script

This way it's easier for users to follow the status of pending issues
with each release.
diff --git a/scripts/announce-release b/scripts/announce-release
index 90a36c0..972d6ea 100755
--- a/scripts/announce-release
+++ b/scripts/announce-release
@@ -156,6 +156,7 @@
  echo "   Site index       : http://www.haproxy.org/"
  echo "   Discourse        : http://discourse.haproxy.org/"
  echo "   Slack channel    : https://slack.haproxy.org/"
+ echo "   Issue tracker    : https://github.com/haproxy/haproxy/issues"
  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}"