[x/blog] blog: update README
[x/blog] blog: update README

Change-Id: Id9a469d475a3e429418135b11bc7e7c7063224a5
Reviewed-on: https://go-review.googlesource.com/37722
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
X-Blog-Commit: c9e809dc6ee25498dafae464f0b21bfe7ad1c7ac

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website