docs: add caEventRate cli reference imported from CAref.html

documentation/ca-cli.md

@@ -17,4 +17,5 @@ caput
 acctst
 catime
 casw
+caEventRate
 ```

modules/ca/src/client/Makefile

@@ -15,6 +15,7 @@ HTMLS += CAref.html
 DOCS += acctst.md
 DOCS += catime.md
 DOCS += casw.md
+DOCS += caEventRate.md
 
 #
 #	includes to install from this subproject

modules/ca/src/client/caEventRate.md

@@ -0,0 +1,10 @@
+# caEventRate
+
+    caEventRate <PV name> [subscription count]
+
+## Description
+
+Connect to the specified PV, subscribe for monitor updates the specified
+number of times (default once), and periodically log the current sampled
+event rate, average event rate, and the standard deviation of the event
+rate in Hertz to standard out.