Update README.md theory section; add CI tests #3618

Job	Run time
test (ubuntu-latest, ci)	20m 30s
test (ubuntu-latest, other)	3m 27s
test (ubuntu-latest, third_party_0)	9m 26s
test (ubuntu-latest, third_party_1)	25m 20s
test (ubuntu-latest, trycmd)	2m 53s
test (macos-latest, ci)	2m 27s
test (macos-latest, other)	17m 10s
test (macos-latest, third_party_0)	1h 6m 36s
test (macos-latest, third_party_1)	40m 59s
test (macos-latest, trycmd)	22m 3s
test (windows-latest, ci)	4m 23s
test (windows-latest, other)	7m 0s
test (windows-latest, third_party_0)	16m 41s
test (windows-latest, third_party_1)	31m 59s
test (windows-latest, trycmd)	6m 17s
all-checks	1s
	4h 37m 12s

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