Doc: prefer more specific file name

Change filters.txt to ref-reachability-filters.txt in order to avoid
squatting on a file name that might be useful for another purpose.

Signed-off-by: Aaron Lipman <alipman88@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -368,7 +368,7 @@ serve four related but different purposes:
 - `--no-merged` is used to find branches which are candidates for merging
   into HEAD, since those branches are not fully contained by HEAD.
 
-include::filters.txt[]
+include::ref-reachability-filters.txt[]
 
 SEE ALSO
 --------

Documentation/git-for-each-ref.txt

@@ -409,7 +409,7 @@ will be reported.
 NOTES
 -----
 
-include::filters.txt[]
+include::ref-reachability-filters.txt[]
 
 SEE ALSO
 --------

Documentation/git-tag.txt

@@ -380,7 +380,7 @@ include::date-formats.txt[]
 NOTES
 -----
 
-include::filters.txt[]
+include::ref-reachability-filters.txt[]
 
 SEE ALSO
 --------