config.txt: move showBranch.* to a separate file

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -407,9 +407,7 @@ include::config/sendemail.txt[]
 
 include::config/sequencer.txt[]
 
-showBranch.default::
-	The default set of branches for linkgit:git-show-branch[1].
-	See linkgit:git-show-branch[1].
+include::config/showbranch.txt[]
 
 splitIndex.maxPercentChange::
 	When the split index feature is used, this specifies the

Documentation/config/showbranch.txt

@@ -0,0 +1,3 @@
+showBranch.default::
+	The default set of branches for linkgit:git-show-branch[1].
+	See linkgit:git-show-branch[1].