MXS-1467: Add csmon documentation

Added documentation for the monitor.

Documentation/Monitors/ColumnStore-Monitor.md

@@ -0,0 +1,53 @@
+# ColumnStore Monitor
+
+The ColumnStore monitor, `csmon`, is a monitor module for MariaDB ColumnStore
+servers. It supports multiple UM nodes and can detect the correct server for
+DML/DDL statements which will be labeled as the master. Other UM nodes will be
+used for reads.
+
+## Master Selection
+
+The automatic master detection only works with ColumnStore 1.1.7 (planned
+version at the time of writing). Older versions of ColumnStore do not implement
+the required functionality to automatically detect which of the servers is the
+primary UM.
+
+With older versions the `primary` parameter must be defined to tell the monitor
+which of the servers is the primary UM node. This guarantees that DDL statements
+are only executed on the primary UM.
+
+## Configuration
+
+Read the [Monitor Common](Monitor-Common.md) document for a list of supported
+common monitor parameters.
+
+### `primary`
+
+The `primary` parameter controls which server is chosen as the master
+server. This is an optional parameter.
+
+If the server pointed to by this parameter is available and is ready to process
+queries, it receives the _Master_ status. If the parameter is not defined and
+the ColumnStore server does not support the `mcsSystemPrimary` function, no
+master server is chosen.
+
+Note that this parameter is only used when the server does not implement the
+required functionality. Otherwise the parameter is ignored as the information
+from ColumnStore itself is more reliable.
+
+## Example
+
+The following is an example of a `csmon` configuration.
+
+```
+[CS-Monitor]
+type=monitor
+module=csmon
+servers=um1,um2,um3
+user=myuser
+passwd=mypwd
+monitor_interval=5000
+primary=um1
+```
+
+It defines a set of three UMs and defines the UM `um1` as the primary UM.