Add short explanation of how MRs and release builds are working

README.md

@@ -69,3 +69,17 @@ from the LHCb environment LbEnv) and make sure to install the hooks in the Git c
 ```
 pre-commit install
 ```
+
+## Merge Requests and Release Builds
+
+When a *ready* merge request (non-draft) is available, the nightly builds system picks it
+up and triggers a build of all projects that are defined in the slot and not already
+available on CVMFS.
+
+The *release shifter* on duty will pick up the MR and complete the deployment of the
+projects following the check list pre-filled in the merge request description. Once all
+tasks are completed, the MR can be merged.
+
+If there is a problem during with the release build, the MR should be marked as *draft*
+until the problem is resolved. A new build will be automatically triggered once the
+merge request is marked again as *ready* (provided it stayed *draft* for at least 10 minutes).