Add curl example using protobuf format to wiki

[leighmcculloch]

The wiki has an example of how to curl using the json format here:
https://github.com/twitchtv/twirp/wiki/HTTP-Routing-and-Serialization#making-requests-on-the-command-line-with-curl

It would be useful I think if this section also contained an example of how to curl using protobuf, which is possible if the user has protoc installed, which is likely since it's required for building the autogenerated code.

e.g.

echo "inches:10" \
	| protoc --proto_path=$GOPATH/src --encode twirp.example.haberdasher.Size ./rpc/haberdasher/service.proto \
	| curl -s --request POST --header "Content-Type: application/protobuf" --data-binary @- http://localhost:8080/twirp/twirp.example.haberdasher.Haberdasher/MakeHat \
	| protoc --proto_path=$GOPATH/src --decode twirp.example.haberdasher.Hat ./rpc/haberdasher/service.proto

I'd open a PR to add it to docs, but I don't see a way of doing that since the docs are in the github wiki and not in the repo.

[spenczar]

Wow, this is pretty cool. I think this is worth putting somewhere, but I'm not totally sure where just yet.

Let's wait until we have some better-structured docs, which should come via #1 - I'd like to move off the wiki, it's hard for people to contribute to.

[leighmcculloch]

#1 is closed now, where's the right place to open a PR for this change?

[spenczar]

Right, sorry about that. I've got a new pass at docs, #75, which I plan to merge today, hold tight.

[leighmcculloch]

@spenczar Still worth including this in the docs? Or should we close this?

[leighmcculloch]

Also, new docs look great 😄.

[spenczar]

Yeah, it's still worth adding this somewhere - it's just such a good trick.

[leighmcculloch]

@spenczar Added a doc page containing JSON and Protobuf examples for cURLing in #109.