io: add example for Pipe
io: add example for Pipe

Change-Id: I24374accf48d43edf4bf27ea6ba2245ddca558ad
Reviewed-on: https://go-review.googlesource.com/50910
Reviewed-by: Giovanni Bajo <387225cd66f97dc812a00599dbc5b6544a73295c@develer.com>
Reviewed-by: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>
Run-TryBot: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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