Add opam-0install to other tools in README #43

Job	Run time
lower-bounds-downgrade (ubuntu-latest, 4.14.x)	15s
lower-bounds-downgrade (macos-latest, 4.14.x)	18s
opam-install (ubuntu-latest, 4.14.x)	15s
build (ubuntu-latest, 4.13.x)	16s
build (ubuntu-latest, 5.1.x)	19s
build (ubuntu-latest, 4.11.x)	14s
opam-install (macos-latest, 4.14.x)	20s
build (ubuntu-latest, 4.14.x)	16s
build (ubuntu-latest, 5.0.x)	16s
build (ubuntu-latest, 4.10.x)	17s
build (ubuntu-latest, 4.09.x)	14s
build (ubuntu-latest, 4.12.x)	17s
build (ubuntu-latest, 4.08.x)	14s
	3m 31s

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