doc: Add installation instructions for GitHub releases #865

Job	Run time
AutoReview Tests	18s
Lint CS	24s
Unit Tests (PHP 8.1, locked)	23s
Unit Tests (PHP 8.1, lowest)	34s
Unit Tests (PHP 8.1, highest)	22s
Update the RequirementChecker	0s
Unit Tests (PHP 8.2, highest)	31s
Unit Tests (PHP 8.3, highest, --ignore-platform-req=php+)	53s
Wait for the PHAR & Docker images	6m 35s
End-to-End Tests (_test_e2e_pass_no_config_min_composer_php, ghcr.io/box-project/box_php725)	37s
End-to-End Tests (_test_e2e_pass_no_config_min_box_php, ghcr.io/box-project/box_php81)	23s
End-to-End Tests (_test_e2e_pass_complete_min_composer_php, ghcr.io/box-project/box_php725)	17s
End-to-End Tests (_test_e2e_pass_complete_min_box_php, ghcr.io/box-project/box_php81)	24s
End-to-End Tests (_test_e2e_fail_complete_min_composer_php, ghcr.io/box-project/box_php725)	32s
End-to-End Tests (_test_e2e_fail_complete_min_box_php, ghcr.io/box-project/box_php81)	31s
End-to-End Tests (_test_e2e_skip_min_composer_php, ghcr.io/box-project/box_php725)	17s
End-to-End Tests (_test_e2e_pass_complete_requirement_checker_not_disabled, ghcr.io/box-project/b...	34s
End-to-End Tests (_test_e2e_fail_conflict, ghcr.io/box-project/box_php81)	32s
RequirementChecker status	1s
	14m 8s

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