add licence info for pypi

Author: lionel42

setup.cfg

@@ -5,6 +5,8 @@ author = Lionel42
 description = A matplotlib backend using pygame.
 long_description = file: README.md
 long_description_content_type = text/markdown
+license = MIT
+license_file = LICENSE
 url = https://github.com/lionel42/pygame-matplotlib-backend
 project_urls =
     Source Code = https://github.com/lionel42/pygame-matplotlib-backend