added C example

// Simple C program to display "Hello World"

// Header file for input output functions

#include <stdio.h>

// main function -

// where the execution of program begins

int main()

{

    // prints hello world

    printf("Hello World");

    return 0;

}

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#!/usr/bin/env bash

rm -rf build

rm -rf dist

#python setup.py build_ext --inplace

python setup.py build_ext

#python setup.py install

python setup.py sdist

pip install dist/*.tar.gz --force-reinstall

    #                   'astropy',

    #                   ],

    python_requires='>=3.9',

    ext_modules=[

        setuptools.Extension(

            name="csst_proto.cext.helloworld", sources=["cextern/helloworld.c"]

        )

    ]

)

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