hash: add marshaling, unmarshaling example
hash: add marshaling, unmarshaling example

Example usage of functionality implemented in CL 66710.

Change-Id: I87d6e4d2fb7a60e4ba1e6ef02715480eb7e8f8bd
Reviewed-on: https://go-review.googlesource.com/76011
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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