Update changelog

README.md

@@ -55,3 +55,13 @@ Sets up the ICSS handling hook.
 ### unregister()
 
 Removes the ICSS handling hook, essentially disabling the module.
+
+## Changelog
+
+### v1.0.0 (February 17, 2021)
+
+- Now actually properly validates arguments, with useful error messages.
+
+### v0.1.0 (February 17, 2021)
+
+Initial release.