DOCS-46 expand a bit on what logRotate does

Author: Ed Costello

source/reference/command/logRotate.txt

@@ -23,7 +23,12 @@ logRotate
 
        kill -SIGUSR1 2200
 
-   The rotated files will have a timestamp of the form ``YYYY-MM-DD``\T ``HH-MM-SS`` 
+
+   :dbcommand:`logRotate` will cause the existing log file to be renamed
+   by appending the current timestamp to the filename.  A new log file will be created
+   with the name which was specified by the :option:`--logpath` option to :program:`mongod` 
+   or :program:`mongos`.
+   The rotated files will have a timestamp of the form yyyy-mm-ddThh-mm-ss 
    appended to the filename.