Introducing CONTRIBUTING.md #696

Job	Run time
PHPUnit Composer v2 (PHP 7.4)	29s
PHPUnit (PHP 7.2)	34s
PHPUnit (PHP 7.3)	36s
Tests alternative autoloader (PHP 7.1)	14s
PHPUnit (PHP 7.4)	37s
Tests alternative autoloader (PHP 7.2)	6s
PHPUnit coverage (PHP 7.4)	1m 21s
PHPUnit (PHP 8.0)	37s
Tests alternative autoloader (PHP 7.3)	15s
PHPUnit (PHP 8.1)	31s
Tests alternative autoloader (PHP 7.4)	7s
PHPUnit (PHP 8.2)	41s
PHPUnit (PHP 7.1)	32s
PHPUnit (PHP 8.3)	47s
Tests alternative autoloader (PHP 8.0)	14s
PHPUnit (PHP 8.4)	29s
Tests alternative autoloader (PHP 8.1)	6s
Tests alternative autoloader (PHP 8.2)	7s
Tests alternative autoloader (PHP 8.3)	15s
PHPUnit lowest deps (PHP 7.3)	31s
Tests alternative autoloader (PHP 8.4)	7s
Windows-Tests with PHP 7.1	1m 12s
Windows-Tests with PHP 7.2	1m 0s
Windows-Tests with PHP 7.3	57s
Windows-Tests with PHP 7.4	59s
Windows-Tests with PHP 8.0	54s
Windows-Tests with PHP 8.1	54s
Windows-Tests with PHP 8.2	58s
Windows-Tests with PHP 8.3	53s
Windows-Tests with PHP 8.4	53s
	17m 56s

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