Update doc to use cm-12.0 instead of 11.0 for cm-12.0 branch

Change-Id: Icfc92fb373506be24b6d73c2235dacca49acc640

README.mkdn

@@ -11,7 +11,7 @@ You can do this by using these commands:
     (Go to repo you are patching, make your changes and commit)
     cmgerrit <for(new)/changes(patch set)> <branch/change-id> 
 
-    repo start cm-11.0 .
+    repo start cm-12.0 .
     (Make your changes and commit)
     repo upload .
 Note: "." meaning current directory
@@ -31,7 +31,7 @@ familiar with [Git and Repo](http://source.android.com/source/using-repo.html).
 
 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-11.0
+    repo init -u git://github.com/CyanogenMod/android.git -b cm-12.0
 
 Then to sync up: