cmd/test2json: document time.Time JSON format
cmd/test2json: document time.Time JSON format

This is already documented in the time.Time package
but people might not look there.

Followup to CL 76872, which I submitted accidentally
(Gerrit has placed the Submit button next to Reply again.)

Change-Id: Ibfd6a4da241982d591a8698282a0c15fe9f2e775
Reviewed-on: https://go-review.googlesource.com/77010
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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