docs: Add upgrade instruction #189

Job	Run time
PHP CS FIXER	24s
unit (8.1, lowest, ubuntu-latest)	15s
integration (8.1, lowest, ubuntu-latest)	1m 40s
unit (8.1, lowest, windows-latest)	55s
unit (8.1, highest, ubuntu-latest)	24s
integration (8.1, lowest, macos-latest)	2m 20s
unit (8.1, highest, windows-latest)	48s
integration (8.1, lowest, windows-latest)	5m 2s
unit (8.2, lowest, ubuntu-latest)	24s
integration (8.1, highest, ubuntu-latest)	1m 5s
unit (8.2, lowest, windows-latest)	48s
integration (8.1, highest, macos-latest)	2m 18s
unit (8.2, highest, ubuntu-latest)	25s
integration (8.1, highest, windows-latest)	5m 10s
unit (8.2, highest, windows-latest)	45s
integration (8.2, lowest, ubuntu-latest)	1m 31s
unit (8.3, lowest, ubuntu-latest)	17s
integration (8.2, lowest, macos-latest)	3m 0s
unit (8.3, lowest, windows-latest)	44s
integration (8.2, lowest, windows-latest)	5m 43s
unit (8.3, highest, ubuntu-latest)	19s
integration (8.2, highest, ubuntu-latest)	2m 0s
unit (8.3, highest, windows-latest)	48s
integration (8.2, highest, macos-latest)	2m 7s
integration (8.2, highest, windows-latest)	5m 36s
integration (8.3, lowest, ubuntu-latest)	1m 3s
integration (8.3, lowest, macos-latest)	2m 1s
integration (8.3, lowest, windows-latest)	5m 29s
integration (8.3, highest, ubuntu-latest)	4m 41s
integration (8.3, highest, macos-latest)	2m 1s
integration (8.3, highest, windows-latest)	5m 53s
	1h 5m 56s

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