[BI] Change --sampleSize help output to say "per namespace" instead of "per database" (#250)

Author: steveren

source/includes/options-mongosqld.yaml

@@ -168,7 +168,7 @@ args: <number>
 description: |
   .. versionadded:: 2.3
 
-  The number of documents per database to sample when gathering schema
+  The number of documents per namespace to sample when gathering schema
   information.
   
   Set :option:`--sampleSize` to ``0`` to include all