Update ZMQ Message Reference

ZMQ-Message-Reference.md

@@ -367,6 +367,17 @@ msg2 = ['modified zonePlate definition',
 
 ## 'oscilloscopeDefinition'
 
+Parameters describing the function of the oscilloscope view of periodic detector readings. Data is a dictionary with the following fields:
+* "on": Boolean integer stating whether the detector readings will be published.
+* "interval": Float value for the time period (seconds) between detector values being published (min. allowed value is 0.1s).
+* "countRate": Boolean integer stating whether the published values are per second (1/True), or raw detector values (0/False)
+
+Example:
+```
+['oscilloscopeDefinition', {'countRate': 1, 'interval': 1.0, 'on': 0}]
+```
+
+
 ## 'focusType'
 
 ## 'scanTypeArchive'