Update ZMQ Message Reference

ZMQ-Message-Reference.md

@@ -72,6 +72,30 @@ Reply Messages:
 * `"lowerSoftLimit"`
 * `"autoOff"`
 
+Example message contents for modifying the CoarseX positioner:
+
+    msg = ['modified positioner definition',
+    '{
+	"name":"CoarseX",
+	"atPositionCheckInterval":0.0020,
+	"atPositionCheckTimeout":10.0,
+	"autoOffMode":"Always",
+	"axisName":"CoarseX",
+	"beamlineControlPosition":0,
+	"coarsePositioner":"",
+	"description":"",
+	"distributionMode":"n",
+	"finePositioner":"",
+	"hardwareUnitFactor":1.0,
+	"lowerSoftLimit":120.0,
+	"maxVelocity":0.0,
+	"positionOffset":3.456,
+	"unit":"()",
+	"upperSoftLimit":1221.0,
+	"velocityUnit":"(/ms)"
+	}']
+
+
 Successful modification of the positioner definition will result in the publication of the new positioner definition in full.
 
 ## 'modified zonePlate definition'