backfill: add builtin boilerplate

In anticipation of implementing 'git backfill', populate the necessary files
with the boilerplate of a new builtin. Mark the builtin as experimental at
this time, allowing breaking changes in the near future, if necessary.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-backfill.txt

@@ -0,0 +1,25 @@
+git-backfill(1)
+===============
+
+NAME
+----
+git-backfill - Download missing objects in a partial clone
+
+
+SYNOPSIS
+--------
+[synopsis]
+git backfill [<options>]
+
+DESCRIPTION
+-----------
+
+THIS COMMAND IS EXPERIMENTAL. ITS BEHAVIOR MAY CHANGE IN THE FUTURE.
+
+SEE ALSO
+--------
+linkgit:git-clone[1].
+
+GIT
+---
+Part of the linkgit:git[1] suite

Documentation/meson.build

@@ -6,6 +6,7 @@ manpages = {
   'git-apply.txt' : 1,
   'git-archimport.txt' : 1,
   'git-archive.txt' : 1,
+  'git-backfill.txt' : 1,
   'git-bisect.txt' : 1,
   'git-blame.txt' : 1,
   'git-branch.txt' : 1,