bytes: add examples for TrimLeft and TrimRight
bytes: add examples for TrimLeft and TrimRight

Change-Id: Ib6d94f185dd43568cf97ef267dd51a09f43a402f
Reviewed-on: https://go-review.googlesource.com/51391
Reviewed-by: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>
Run-TryBot: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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