Ruby

Add doc for Generating RBS #4011

Job	Run time
windows (windows-2019, ucrt)	1m 13s
test (master-nightly-focal, test)	3m 1s
windows (windows-2019, mswin)	48s
test (master-nightly-focal, stdlib_test)	3m 48s
windows (windows-2022, ucrt)	1m 30s
test (master-nightly-focal, rubocop validate test_doc build test_generate_stdlib)	2m 49s
windows (windows-2022, mswin)	1m 0s
test (master-nightly-focal, lexer confirm_lexer)	4m 57s
test (master-nightly-focal, lexer compile)	3m 21s
test (3.2-dev-focal, test)	2m 47s
test (3.2-dev-focal, stdlib_test)	2m 52s
test (3.2-dev-focal, rubocop validate test_doc build test_generate_stdlib)	1m 59s
test (3.2-dev-focal, lexer confirm_lexer)	4m 51s
test (3.2-dev-focal, lexer compile)	3m 18s
test (3.1-dev-focal, test)	2m 48s
test (3.1-dev-focal, rubocop validate test_doc build test_generate_stdlib)	3m 41s
test (3.1-dev-focal, lexer confirm_lexer)	3m 15s
test (3.1-dev-focal, lexer compile)	3m 17s
test (3.0-dev-focal, test)	2m 5s
test (3.0-dev-focal, rubocop validate test_doc build test_generate_stdlib)	2m 3s
test (3.0-dev-focal, lexer confirm_lexer)	5m 13s
test (3.0-dev-focal, lexer compile)	4m 12s
	1h 4m 48s

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