sdl-config: not found

I try to install the requirements, and this fails while installing `pygame`

```
(soclone) guettli@yoga15:~/projects/soclone/src/StackOverFlow-Clone$ pip install -r requirements.txt
Collecting asgiref==3.2.10
Using cached asgiref-3.2.10-py3-none-any.whl (19 kB)
Collecting astroid==2.4.2
Downloading astroid-2.4.2-py3-none-any.whl (213 kB)
|████████████████████████████████| 213 kB 4.5 MB/s
Collecting colorama==0.4.3
Using cached colorama-0.4.3-py2.py3-none-any.whl (15 kB)
Collecting Django==3.1
Downloading Django-3.1-py3-none-any.whl (7.8 MB)
|████████████████████████████████| 7.8 MB 5.6 MB/s
Collecting django-email-verification==0.0.7
Downloading django_email_verification-0.0.7-py3-none-any.whl (7.7 kB)
Collecting isort==4.3.21
Downloading isort-4.3.21-py2.py3-none-any.whl (42 kB)
|████████████████████████████████| 42 kB 1.2 MB/s
Collecting lazy-object-proxy==1.4.3
Downloading lazy_object_proxy-1.4.3-cp38-cp38-manylinux1_x86_64.whl (58 kB)
|████████████████████████████████| 58 kB 5.3 MB/s
Collecting mccabe==0.6.1
Downloading mccabe-0.6.1-py2.py3-none-any.whl (8.6 kB)
Collecting mypy==0.782
Using cached mypy-0.782-cp38-cp38-manylinux1_x86_64.whl (21.7 MB)
Collecting mypy-extensions==0.4.3
Using cached mypy_extensions-0.4.3-py2.py3-none-any.whl (4.5 kB)
Collecting Pillow==7.2.0
Using cached Pillow-7.2.0-cp38-cp38-manylinux1_x86_64.whl (2.2 MB)
Collecting pygame==1.9.6
Downloading pygame-1.9.6.tar.gz (3.2 MB)
|████████████████████████████████| 3.2 MB 10.2 MB/s
ERROR: Command errored out with exit status 1:
command: /home/guettli/projects/soclone/bin/python3 -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-780vmvxy/pygame/setup.py'"'"'; __file__='"'"'/tmp/pip-install-780vmvxy/pygame/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-install-780vmvxy/pygame/pip-egg-info
cwd: /tmp/pip-install-780vmvxy/pygame/
Complete output (12 lines):


WARNING, No "Setup" File Exists, Running "buildconfig/config.py"
Using UNIX configuration...

/bin/sh: 1: sdl-config: not found
/bin/sh: 1: sdl-config: not found
/bin/sh: 1: sdl-config: not found

Hunting dependencies...
WARNING: "sdl-config" failed!
Unable to run "sdl-config". Please make sure a development version of SDL is installed.
----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.
```

Why is pygame needed?

Start with requirements.txt and reproduce the failure using pip install -r requirements.txt. Search the project for references to pygame and the sdl-config requirement; done means the dependency's purpose is established and the installation guidance or dependency list reflects that finding.

Written by the indexing model from the issue text.