dpkg-source(1): Improve git format documentation

Based-on-patch-by: Tanguy Ortolo
Signed-off-by: Guillem Jover <guillem@debian.org>

debian/changelog

@@ -3,6 +3,8 @@ dpkg (1.15.8.5) UNRELEASED; urgency=low
   * Do not print a warning when parsing status or status log files on
     half-installed packages w/o a Description or Maintainer field, as
     this happens normally when the package was never installed before.
+  * Improve git format documentation in dpkg-source(1).
+    Thanks to Joey Hess, based on a patch by Tanguy Ortolo.
 
  -- Guillem Jover <guillem@debian.org>  Sat, 21 Aug 2010 08:09:39 +0200
 

man/dpkg-source.1

@@ -555,12 +555,18 @@ The generated .dsc file will contain this value in its \fIFormat\fP field
 and not "3.0 (custom)".
 .
 .SS Format: 3.0 (git)
-This format is experimental. It uses a bundle of a git repository to hold
-the source of a package.
+This format is experimental.
+.PP
+A source package in this format consists of a
+single bundle of a git repository \fB.git\fP to hold the source of a package.
+There may also be a \fB.gitshallow\fP file listing revisions for a shallow
+git clone.
 .PP
 .B Extracting
 .PP
-The bundle is cloned to a new git repository.
+The bundle is cloned as a git repository to the target directory.
+If there is a gitshallow file, it is installed as `.git/shallow` inside
+the cloned git repository.
 .PP
 Note that by default the new repository will have the same branch checked
 out that was checked out in the original source. (Typically "master", but