docs/configuration: Add smv_prefer_remote_refs option

docs/configuration.rst

@@ -26,6 +26,9 @@ This is what the default configuration looks like:
     # Format for versioned output directories inside the build directory
     smv_outputdir_format = '{ref.name}'
 
+    # Determines whether remote or local git branches/tags are preferred if their output dirs conflict
+    smv_prefer_remote_refs = False
+
 You an override all of these values inside you :file:`conf.py`.
 
 .. note::