[DOC] Doc for StringIO#read #564

Job	Run time
ruby-versions / Generate Ruby versions	4s
windows-latest 3.1	1m 28s
windows-latest 2.7	2m 1s
windows-latest 3.0	1m 37s
windows-latest 3.2	1m 29s
windows-latest 3.3	1m 26s
windows-latest jruby-head	2m 5s
windows-latest mingw	1m 39s
windows-latest mswin	1m 29s
windows-latest 3.4	1m 30s
	14m 48s

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