Add a note about finding incompatibilities

Author: coolreader18

_posts/2021-01-27-pip-support.markdown

@@ -34,6 +34,10 @@ This update is brought to you from [@coolreader18's](https://github.com/coolread
     pip 21.0 from /home/.../.local/lib/rustpython3.9/site-packages/pip (python 3.9)
 ```
 
+There's undoubtedly still a lot that doesn't work, so if there's something simple-ish that errors inside of pip or a setup script, feel free to open an issue for it (note that C extensions won't be supported anytime soon, and a ctypes implementation is in progress).
+
+(Previous instructions):
+
 This update is so fresh, things are not merged into the `master` or `release` branches yet. For now, to test this out, you have to checkout the `pip-merg` branch, and make sure to build with the `ssl` feature:  
 
 ```shell