[DOC] Doc for StringIO#each (#154) #464

Job	Run time
ruby-versions / Generate Ruby versions	5s
windows-latest 2.7	1m 38s
windows-latest 3.3	1m 25s
windows-latest mingw	1m 0s
windows-latest 3.4	1m 3s
windows-latest 3.0	1m 7s
windows-latest 3.2	1m 23s
windows-latest jruby-head	1m 37s
windows-latest 3.1	58s
windows-latest mswin	1m 30s
	11m 46s

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