add a known issues section

README.md

@@ -469,6 +469,11 @@ require "dep" {
 }
 ```
 
+## Known Issues
+
+- Lazy loading nvim-cmp doesn't work as the external sources don't get reconized
+by nvim-cmp when it's loaded.
+
 ## License
 
 dep is licensed under the [MIT License](LICENSE).