gitlab migration intro

tsa/howto/gitlab.mdwn

@@ -57,6 +57,14 @@ There is also a config backup job that makes sure to backup the content of
 
 ## Migration
 
+GitLab was migrated from Trac in June 2020, after a few months of
+testing. Tests were done first on a server called
+`dip.torproject.org`, a reference to `salsa.debian.org`, the GitLab
+server ran by the Debian project. We identified [some problems with
+merge requests](https://gitlab.torproject.org/tpo/tpa/services/-/issues/32197) during the test so the server was reinstalled with
+the "GitLab Omnibus" package on the current server, `gitlab-02` which
+will enter production in the week of June 15th 2020.
+
 ### Migrated content
 
 The issues and wiki of the "Tor" project are migrated. There are no