DOCS-953 release notes edits to text search info

Author: kay-kim

source/release-notes/2.4.txt

@@ -82,16 +82,17 @@ support boolean text search queries:
 However, ``text`` indexes have large storage requirements and incur
 **significant** performance costs:
 
-- Text indexes can be large.  They contain one index entry for each
-  unique word indexed for each document inserted.
+- Text indexes can be large. They contain one index entry for each
+  unique post-stemmed word in each indexed field for each document
+  inserted.
 
 - Building a ``text`` index is very similar to building a large
   multi-key index, and therefore may take longer than building a
   simple ordered (scalar) index.
 
 - ``text`` indexes will impede insertion throughput, because MongoDB
-  must add an index entry for each unique word in each indexed field of
-  each new source document.
+  must add an index entry for each unique post-stemmed word in each
+  indexed field of each new source document.
 
 - some :dbcommand:`text` searches may affect performance on your
   :program:`mongod`, particularly for negation queries and phrase