add toc on index #31

Job	Run time
lint	18s
ruby-versions / Generate Ruby versions	3s
test (3.0, ubuntu-latest)	24s
test (3.0, macos-latest)	21s
test (3.0, windows-latest)	1m 18s
test (3.1, ubuntu-latest)	32s
test (3.1, macos-latest)	22s
test (3.1, windows-latest)	1m 16s
test (3.2, ubuntu-latest)	23s
test (3.2, macos-latest)	22s
test (3.2, windows-latest)	1m 24s
test (3.3, ubuntu-latest)	33s
test (3.3, macos-latest)	20s
test (3.3, windows-latest)	1m 45s
test (head, ubuntu-latest)	44s
test (head, macos-latest)	24s
test (head, windows-latest)	1m 18s
test (jruby, ubuntu-latest)	2m 4s
test (jruby, macos-latest)	1m 50s
test (jruby-head, ubuntu-latest)	1m 54s
test (jruby-head, macos-latest)	1m 38s
test (truffleruby, ubuntu-latest)	2m 30s
test (truffleruby, macos-latest)	1m 43s
test (truffleruby-head, ubuntu-latest)	3m 19s
test (truffleruby-head, macos-latest)	2m 23s
	29m 8s

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