Update ZMQ Message Reference

ZMQ-Message-Reference.md

@@ -1,13 +1,43 @@
 This page lists the JSON strings that can be sent to the ZMQ REQ/REP port in order to request actions by Pixelator. The ZMQ messages must be sent in the format:
 
-`[HEADER, {"key1":"value1","key2":"value2","key3":"value3"}]`
+`[HEADER, DATA1 (, DATA2)]`
+
+where the data can either be an empty string, or a JSON structure, e.g.:
+
+`{"key1":"value1","key2":"value2","key3":"value3"}`
 
 Request messages are typically responded to by a simple `["status", "ok"]` response on the REQ/REP port and the publication of further data on the PUB/SUB port.
 
 ## 'initialize'
 
+No data required or used. Lots of data is returned and published with the intended use being to populate a GUI.
+
+Reply Messages:
+- `["status","ok"]`
+- Positioner definitions
+- Detector definitions
+- Oscilloscope options
+- Zone Plate definitions
+- File IO config options
+
+Published Messages:
+- Positioner status
+- Focus status
+- Scan status
+- Beam shutter status
+- Topup status
+- User status
+- Recorded channels
+- Focus type
+- Scan type archive attribute
+- Beam shutter mode
+- Topup mode
+
 ## 'recordedChannels'
 
+Reply Messages:
+- `["status","ok"]`
+
 ## 'detectorSettings'
 
 ## 'updateDetectorSettings'