Fix documentation of hashtag: search predicate

The hashtag: search is case-insensitive, but the documentation said
it was an exact match.

Bug: Issue 10564
Change-Id: I14882fdc1ed2c45b10387b0f4e80cd195caee37c
diff --git a/Documentation/user-search.txt b/Documentation/user-search.txt
index fbf78a3..21875b2 100644
--- a/Documentation/user-search.txt
+++ b/Documentation/user-search.txt
@@ -201,7 +201,8 @@
 [[hashtag]]
 hashtag:'HASHTAG'::
 +
-Changes whose link:intro-user.html#hashtags[hashtag] matches 'HASHTAG' exactly.
+Changes whose link:intro-user.html#hashtags[hashtag] matches 'HASHTAG'.
+The match is case-insensitive.
 
 [[ref]]
 ref:'REF'::