README: Add description of master branch

Add info about the master branch, which is for fixes for the current
release, and elaborate about what the branches are based on.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
diff --git a/README b/README
index 5fe38ce..4226600 100644
--- a/README
+++ b/README
@@ -12,6 +12,19 @@
 
 The main branches are as follows:
 
+master:
+	This branch contains the queue of KVM/MIPS fixes for the current
+	release, based on the master branch of:
+
+	git://git.kernel.org/pub/scm/virt/kvm/kvm.git
+
+	This branch may occasionally be rebased, and may be merged into the next
+	branch.
+
 next:
-	This branch contains the queue of KVM/MIPS patches for the next release.
+	This branch contains the queue of KVM/MIPS patches for the next release
+	(including fixes for the current release), based on the next branch of:
+
+	git://git.kernel.org/pub/scm/virt/kvm/kvm.git
+
 	This branch may occasionally be rebased, and is included in linux-next.