forum: add info how to mirror a mailinglist

service/forum.md

@@ -12,6 +12,14 @@ benefit of the Tor community.
 
 # How-to
 
+## Mirror a mailing list
+
+The instructions to set up a mirror for a mailing list can be found
+[here](https://meta.discourse.org/t/creating-a-read-only-mailing-list-mirror/77990#category-2).
+
+The address used for delivering emails into our Discourse instance is
+`torproject1@discoursemail.com`.
+
 ## Pager playbook
 
 In case of a problem with the forum, we should start by checking the Discouse