config.txt: move alias.* 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

@@ -293,24 +293,7 @@ include::config/core.txt[]
 
 include::config/add.txt[]
 
-alias.*::
-	Command aliases for the linkgit:git[1] command wrapper - e.g.
-	after defining "alias.last = cat-file commit HEAD", the invocation
-	"git last" is equivalent to "git cat-file commit HEAD". To avoid
-	confusion and troubles with script usage, aliases that
-	hide existing Git commands are ignored. Arguments are split by
-	spaces, the usual shell quoting and escaping is supported.
-	A quote pair or a backslash can be used to quote them.
-+
-If the alias expansion is prefixed with an exclamation point,
-it will be treated as a shell command.  For example, defining
-"alias.new = !gitk --all --not ORIG_HEAD", the invocation
-"git new" is equivalent to running the shell command
-"gitk --all --not ORIG_HEAD".  Note that shell commands will be
-executed from the top-level directory of a repository, which may
-not necessarily be the current directory.
-`GIT_PREFIX` is set as returned by running 'git rev-parse --show-prefix'
-from the original current directory. See linkgit:git-rev-parse[1].
+include::config/alias.txt[]
 
 am.keepcr::
 	If true, git-am will call git-mailsplit for patches in mbox format

Documentation/config/alias.txt

@@ -0,0 +1,18 @@
+alias.*::
+	Command aliases for the linkgit:git[1] command wrapper - e.g.
+	after defining "alias.last = cat-file commit HEAD", the invocation
+	"git last" is equivalent to "git cat-file commit HEAD". To avoid
+	confusion and troubles with script usage, aliases that
+	hide existing Git commands are ignored. Arguments are split by
+	spaces, the usual shell quoting and escaping is supported.
+	A quote pair or a backslash can be used to quote them.
++
+If the alias expansion is prefixed with an exclamation point,
+it will be treated as a shell command.  For example, defining
+"alias.new = !gitk --all --not ORIG_HEAD", the invocation
+"git new" is equivalent to running the shell command
+"gitk --all --not ORIG_HEAD".  Note that shell commands will be
+executed from the top-level directory of a repository, which may
+not necessarily be the current directory.
+`GIT_PREFIX` is set as returned by running 'git rev-parse --show-prefix'
+from the original current directory. See linkgit:git-rev-parse[1].