[ostree] docs: Reference the git docs on references

[Colin Walters <walters src gnome org>]

commit 89514dd8ba807f10460ddcbb6a033f79706d0d0c
Author: Colin Walters <walters verbum org>
Date:   Wed Mar 9 14:07:52 2016 -0500

    docs: Reference the git docs on references

 docs/manual/repo.md |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)
---
diff --git a/docs/manual/repo.md b/docs/manual/repo.md
index f636d57..3a9e8c9 100644
--- a/docs/manual/repo.md
+++ b/docs/manual/repo.md
@@ -74,9 +74,13 @@ command, it will operate on the system repository.
 
 ## Refs
 
-Like git, OSTree uses "refs" to which are text files that point to
-particular commits (i.e. filesystem trees).  For example, the
-gnome-ostree operating system creates trees named like
+Like git, OSTree uses the terminology "references" (abbreviated
+"refs") which are text files that name (refer to) to particular
+commits.  See the
+[Git Documentation](https://git-scm.com/book/en/v2/Git-Internals-Git-References)
+for information on how git uses them.  Unlike git though, it doesn't
+usually make sense to have a "master" branch.  There is a convention
+for references in OSTree that looks like this:
 `exampleos/buildmaster/x86_64-runtime` and
 `exampleos/buildmaster/x86_64-devel-debug`.  These two refs point to
 two different generated filesystem trees.  In this example, the