DOC Add composer install command and repository link #500

Job	Run time
ci / Context	2s
ci / Generate matrix	19s
ci / Check governance	4s
ci / 8.3 mysql80 phpunit all	7m 56s
ci / 8.3 mysql84 phpunit all	6m 31s
ci / 8.1 mysql57 endtoend root job1	6m 1s
ci / 8.1 prf-low mysql57 phpunit all	5m 52s
ci / 8.2 mariadb phpunit all	4m 29s
ci / 8.1 mysql57 doclinting	3m 4s
ci / 8.3 mysql80 endtoend root job2	11m 6s
ci / 8.1 mysql57 phplinting	2m 10s
ci / 8.1 mysql57 js	5m 21s
ci / 8.3 mysql80 endtoend root job1	6m 31s
ci / 8.1 mysql57 endtoend root job2	10m 19s
ci / Dispatch tag patch release	-1s
	1h 9m 44s

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