Generalizing services and overrides in linux.system.service
Adding tests for linux.system.service

Prod-Related: PROD-22528

Change-Id: I46ca9a16b35af7f271053c0b6abb2c331f9c4c6b
diff --git a/README.rst b/README.rst
index 0db113f..ab091b8 100644
--- a/README.rst
+++ b/README.rst
@@ -1231,6 +1231,28 @@
           apt-daily.timer:
             status: dead
 
+Override systemd service unit:
+
+.. code-block:: yaml
+
+  parameters:
+
+    linux:
+      system:
+        service:
+          tgt:
+            name: tgt
+            status: running
+            enabled: True
+            override:
+              50:
+                target: tgt.service.d
+                name: bind
+                content: |
+                  [Service]
+                  ExecStart=
+                  ExecStart=/usr/sbin/tgtd -f --iscsi portal=${_param:single_address}:3260
+
 Possible statuses are ``dead`` (disable service by default), ``running``
 (enable service by default), ``enabled``, ``disabled``: