manifest:Update README for CM13

Change-Id: Ibf68fd55cf0ee346512423ece8df1e55f38a3613
diff --git a/README.mkdn b/README.mkdn
index fdbee21..e591dc1 100644
--- a/README.mkdn
+++ b/README.mkdn
@@ -11,7 +11,7 @@
     (Go to repo you are patching, make your changes and commit)
     cmgerrit <for(new)/changes(patch set)> <branch/change-id> 
 
-    repo start cm-12.1 .
+    repo start cm-13.0 .
     (Make your changes and commit)
     repo upload .
 Note: "." meaning current directory
@@ -31,7 +31,7 @@
 
 To initialize your local repository using the CyanogenMod trees, use a command like this:
 
-    repo init -u git://github.com/CyanogenMod/android.git -b cm-12.1
+    repo init -u git://github.com/CyanogenMod/android.git -b cm-13.0
 
 Then to sync up: