Update 'README.md'

README.md

@@ -1 +1,8 @@
-# See [`greenlock-store-test`](https://git.rootprojects.org/root/greenlock-store-test.js)
+# See [`greenlock-store-test`](https://git.rootprojects.org/root/greenlock-store-test.js)
+
+That's the test.
+
+## Reference implementations
+
+* [`greenlock-store-fs`](https://git.rootprojects.org/root/greenlock-store-fs.js)
+* [`greenlock-store-sequelize`](https://git.rootprojects.org/root/greenlock-store-sequelize.js)