strings: add example for IndexByte
strings: add example for IndexByte

Change-Id: Ib6a59735381ce744553f1ac96eeb65a194c8da10
Reviewed-on: https://go-review.googlesource.com/48860
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

akutz/go,josharian/go,polyverse-security/go,akutz/go,golang/go,codestation/go,polyverse-security/go,josharian/go,Cofyc/go,christopher-henderson/Go,codestation/go,josharian/go,polyverse-security/go,golang/go,josharian/go,Cofyc/go,akutz/go,josharian/go,CAFxX/go,nawawi/go,CAFxX/go,golang/go,vsekhar/elastic-go,codestation/go,CAFxX/go,vsekhar/elastic-go,akutz/go,CAFxX/go,josharian/go,akutz/go,cloudflare/go,nawawi/go,akutz/go,nawawi/go,codestation/go,golang/go,golang/go,golang/go,vsekhar/elastic-go,codestation/go,CAFxX/go,cloudflare/go,vsekhar/elastic-go,Cofyc/go,cloudflare/go,vsekhar/elastic-go,polyverse-security/go,Cofyc/go,golang/go,CAFxX/go,polyverse-security/go,cloudflare/go,cloudflare/go,Cofyc/go,codestation/go,polyverse-security/go,golang/go,cloudflare/go,nawawi/go,akutz/go,vsekhar/elastic-go,codestation/go,nawawi/go,cloudflare/go,polyverse-security/go,josharian/go,Cofyc/go,josharian/go,codestation/go,nawawi/go,vsekhar/elastic-go,CAFxX/go,Cofyc/go,nawawi/go,akutz/go,vsekhar/elastic-go,nawawi/go,Cofyc/go,CAFxX/go,cloudflare/go,polyverse-security/go