pygame_shaders depends on moderngl but doesn't automatically install it when it is installed

To Reproduce
Steps to reproduce the behavior:

1. Install the latest version of pygame_shaders directly from Github like here: module 'pygame_shaders' has no attribute 'DefaultScreenShader' #9 (comment)
2. Run import pygame_shaders
3. Results in: ModuleNotFoundError: No module named 'moderngl'
4. which requires a manual pip install moderngl

Expected behavior
For pygame_shaders to list moderngl as a dependency, so it is automatically installed with it