Update README.md

Author: e3ndr

README.md

@@ -8,6 +8,9 @@ A (new!) Java port of the [webview project](https://github.com/webview/webview).
 2) Copy and run the example in `Example.java`.
 3) Profit!
 
+## MacOS
+MacOS requires that all UI code be executed from the first thread, which means you will need to launch Java with `-XstartOnFirstThread`. This also means that the Webview AWT helper will NOT work at all.
+
 ## TODO
 
 Build our own DLLs and whatnot, the current ones are copied from the C# port.