Move the extensions resource to common/.
diff --git a/openstack/common/README.md b/openstack/common/README.md
new file mode 100644
index 0000000..7b55795
--- /dev/null
+++ b/openstack/common/README.md
@@ -0,0 +1,3 @@
+# Common Resources
+
+This directory is for resources that are shared by multiple services.