DOCSP-28108 Add Index Usage Details (#495)

Author: ianf-mongodb

source/indexes.txt

@@ -65,8 +65,8 @@ For each index, Compass displays the following information:
      - How large the index is.
 
    * - Usage
-     - Number of times the index has been used since the time the index
-       was created or the last server restart.
+     - Number of times the index has been used in a lookup since the time
+       the index was created or the last server restart.
 
    * - Properties