Update README.md

Author: treeben77

README.md

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 # DiscordOAuth2.py
 Use Discord's OAuth2 effortlessly! Turns the auth code to a access token and the access token into scope infomation.
 
+> **Notice:** I don't know how to make my library work with `pip install` so you'll have to copy the source code and paste it into your workspace.
+
 ### Using DiscordOAuth2.py with Flask
 You can try out a working example here: https://DiscordOAuth2py.treeben77.repl.co
 ```python