[ostree] manual: Note that the bare-user mode exists

[Colin Walters <walters src gnome org>]

commit 707c14aeebd738c668572f0362cfcfbd94ac4f49
Author: Colin Walters <walters verbum org>
Date:   Thu Feb 18 18:21:32 2016 -0500

    manual: Note that the bare-user mode exists

 docs/manual/repo.md |   25 +++++++++++++++++--------
 1 files changed, 17 insertions(+), 8 deletions(-)
---
diff --git a/docs/manual/repo.md b/docs/manual/repo.md
index a3e64bd..3b7a737 100644
--- a/docs/manual/repo.md
+++ b/docs/manual/repo.md
@@ -49,14 +49,23 @@ header, for regular files, the content follows.
 
 # Repository types and locations
 
-Also unlike git, an OSTree repository can be in one of two separate
-modes: `bare` and `archive-z2`.  A bare repository is one where
-content files are just stored as regular files; it's designed to be
-the source of a "hardlink farm", where each operating system checkout
-is merely links into it.  If you want to store files owned by
-e.g. root in this mode, you must run OSTree as root.  In contrast, the
-`archive-z2` mode is designed for serving via plain HTTP.  Like tar
-files, it can be read/written by non-root users.
+Also unlike git, an OSTree repository can be in one of three separate
+modes: `bare`, `bare-user`, and `archive-z2`.  A bare repository is
+one where content files are just stored as regular files; it's
+designed to be the source of a "hardlink farm", where each operating
+system checkout is merely links into it.  If you want to store files
+owned by e.g. root in this mode, you must run OSTree as root.  
+
+The `bare-user` is a later addition that is like `bare` in that files
+are unpacked, but it can (and should generally) be created as
+non-root.  In this mode, extended metadata such as owner uid, gid, and
+extended attributes are stored but not actually applied.  
+The `bare-user` mode is useful for build systems that run as non-root
+but want to generate root-owned content, as well as non-root container
+systems.
+
+In contrast, the `archive-z2` mode is designed for serving via plain
+HTTP.  Like tar files, it can be read/written by non-root users.
 
 On an OSTree-deployed system, the "system repository" is
 `/ostree/repo`.  It can be read by any uid, but only written by root.