Remove $ from README and update install instructions (#16) #96

Job	Run time
test (ubuntu-latest, 2.7)	53s
test (ubuntu-latest, 3.0)	27s
test (ubuntu-latest, 3.1)	31s
test (ubuntu-latest, head)	1m 21s
test (ubuntu-latest, jruby)	1m 18s
test (ubuntu-latest, jruby-head)	1m 20s
test (ubuntu-latest, truffleruby)	2m 19s
test (ubuntu-latest, truffleruby-head)	2m 41s
test (macos-latest, 2.7)	54s
test (macos-latest, 3.0)	31s
test (macos-latest, 3.1)	33s
test (macos-latest, head)	1m 8s
test (macos-latest, jruby)	1m 8s
test (macos-latest, jruby-head)	1m 20s
test (macos-latest, truffleruby)	1m 49s
test (macos-latest, truffleruby-head)	2m 1s
	20m 14s

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