DOCSP-5582: Clarify wildcard index behavior w.r.t. sharding

Author: ravindk89

source/release-notes/4.2.txt

@@ -438,7 +438,7 @@ Wildcard Index Limitations
   - :query:`{ $ne: { \<object\> } } <$ne>`
   - :query:`{ $ne: null } <$ne>` (for queries on field paths that include arrays)
 
-- You cannot shard a collection using a wildcard index.
+- You cannot shard a collection using a wildcard index as the shard key.
 
 - For queries that specify multiple fields covered by a wildcard index,
   the wildcard index can support at most *one* of the fields in the