Introducing CONTRIBUTING.md (#744) #702

Job	Run time
PHPUnit (PHP 7.2)	32s
PHPUnit coverage (PHP 7.4)	1m 13s
PHPUnit Composer v2 (PHP 7.4)	31s
Tests alternative autoloader (PHP 7.1)	10s
PHPUnit (PHP 7.3)	43s
Tests alternative autoloader (PHP 7.2)	21s
PHPUnit (PHP 7.4)	50s
Tests alternative autoloader (PHP 7.3)	12s
PHPUnit (PHP 8.0)	32s
PHPUnit (PHP 7.1)	41s
PHPUnit lowest deps (PHP 7.3)	36s
Tests alternative autoloader (PHP 7.4)	14s
PHPUnit (PHP 8.1)	39s
Tests alternative autoloader (PHP 8.0)	11s
PHPUnit (PHP 8.2)	48s
Tests alternative autoloader (PHP 8.1)	8s
PHPUnit (PHP 8.3)	27s
Tests alternative autoloader (PHP 8.2)	10s
PHPUnit (PHP 8.4)	54s
Tests alternative autoloader (PHP 8.3)	10s
Windows-Tests with PHP 7.1	1m 15s
Tests alternative autoloader (PHP 8.4)	9s
Windows-Tests with PHP 7.2	55s
Windows-Tests with PHP 7.3	58s
Windows-Tests with PHP 7.4	58s
Windows-Tests with PHP 8.0	1m 0s
Windows-Tests with PHP 8.1	54s
Windows-Tests with PHP 8.2	1m 3s
Windows-Tests with PHP 8.3	55s
Windows-Tests with PHP 8.4	53s
	19m 2s

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