strings: add a example for Compare func
strings: add a example for Compare func

Add a example for string.Compare that return the three possible results.

Change-Id: I103cf39327c1868fb249538d9e22b11865ba4b70
Reviewed-on: https://go-review.googlesource.com/49011
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

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