new: ``ssh-tunnel`` commented example added.

compose.yml

@@ -60,6 +60,14 @@ mydomain.org:
 
 frontend:
   charm: apache
+  # options:
+  #   ## Check 0k-charms/apache/README.rst for client side configuration
+  #   ## to use ssh-tunnel.
+  #   ssh-tunnel:
+  #     domain: ssh.mydomain.org  ## mandatory
+  #     # server-aliases:
+  #     # - ssh2.daowen.eu
+  #     #ssl: letsencrypt
   ## XXXvlab: this is still necessary (although it is auto connected
   ## in most cases) but we require it on some occasion (namely "run"
   ## actions on odoo for instance) until we decide a way to tackle