Introducing CONTRIBUTING.md #701

Job	Run time
PHPUnit (PHP 7.2)	31s
PHPUnit (PHP 7.1)	39s
PHPUnit (PHP 7.3)	32s
PHPUnit (PHP 7.4)	36s
PHPUnit (PHP 8.0)	28s
PHPUnit (PHP 8.1)	30s
PHPUnit (PHP 8.2)	40s
PHPUnit (PHP 8.3)	28s
PHPUnit (PHP 8.4)	30s
Tests alternative autoloader (PHP 7.1)	14s
Tests alternative autoloader (PHP 7.2)	6s
Tests alternative autoloader (PHP 7.3)	7s
Tests alternative autoloader (PHP 7.4)	8s
PHPUnit Composer v2 (PHP 7.4)	33s
Tests alternative autoloader (PHP 8.0)	7s
PHPUnit coverage (PHP 7.4)	1m 1s
Tests alternative autoloader (PHP 8.1)	11s
PHPUnit lowest deps (PHP 7.3)	40s
Tests alternative autoloader (PHP 8.2)	11s
Tests alternative autoloader (PHP 8.3)	18s
Windows-Tests with PHP 7.1	1m 13s
Tests alternative autoloader (PHP 8.4)	8s
Windows-Tests with PHP 7.2	56s
Windows-Tests with PHP 7.3	58s
Windows-Tests with PHP 7.4	57s
Windows-Tests with PHP 8.0	58s
Windows-Tests with PHP 8.1	55s
Windows-Tests with PHP 8.2	56s
Windows-Tests with PHP 8.3	1m 2s
Windows-Tests with PHP 8.4	1m 0s
	17m 33s

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