service/ci.md

@@ -66,6 +66,21 @@ CI. Anything special on top of [the official docs](https://docs.gitlab.com/runne
 
 ### MacOS/Windows
 
+A special machine (currently `chi-node-13`) was built to allow builds
+to run on MacOS and Windows virtual machines. The machine was
+installed in the Cymru cluster (so following
+[new-machine-cymru](howto/new-machine-cymru)). On top of that procedure, the following extra
+steps were taken on the machine:
+
+ 1. a bridge (`br0`) was setup
+ 2. a basic libvirt configuration was built in Puppet (within
+    `roles::gitlab::ci::foreign`)
+
+The `gitlab-ci-admin` role user and group have access to the
+machine. The remaining of the procedure still needs to be implemented
+and documented, here, and eventually converted into a Puppet manifest,
+see [issue #40095](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40095).
+
 TODO: @ahf document how MacOS/Windows images are created and runners
 are setup. don't hesitate to create separate headings for Windows vs
 MacOS and for image creation vs runner setup.