Update protocol buffers blogpost for the deprecation of native Protobuf rules

[Yannic]

Fixes #188

TODO before this can be merged:

• Push updated example to https://github.com/Yannic/proto_library and/or update https://github.com/cgrushko/proto_library
• Fill-in missing fields to load @rules{cc,java,proto}
• Make design doc for Starlark rewrite public and add it to proposals repo
• Ask whether Protobuf can cut a release that includes the changes. They partly agreed to do a Bazel-only release here: Backport Bazel-incompatible fixes to 3.9.x (orginal: #6432) protocolbuffers/protobuf#6438 (comment) (Won't happen until 3.10?)

[Yannic]

This change is ready for review (and for merging by the end of this week).
Thanks in advance

[jin]

cc @lberki

[hlopko]

Hi Yannic, in general, LGTM, I just couldn't for the life of me find the time to render this to verify its clean. Sorry for delays.

[aiuto]

So, where do we stand on this? Do you like the text but want to make sure it renders correctly?
I can do the rendering test.

[aiuto]

It renders fine. Can you add a pointer back to it.

file: _posts/2019-10-01-protobuf-updates.md
======== snip =============

layout: posts
title: "Protobuf instructions update."
authors:

• Yannic

---

Updated instructions for using Protocol Buffers in Bazel
======== snip =============

[Yannic]

@aiuto thanks! done, ptal.

[Yannic]

Friendly ping?