add instructions to install protoc in contributing.md

[moficodes]

What would you like to be added?

add links / instruction to install protoc for setting up the dev environment.

it should also mention that protoc needs to be version 3.20.3 https://github.com/etcd-io/etcd/blob/main/scripts/genproto.sh#L27

Why is this needed?

make verify fails in protoc is not available in the system or the version is anything other than 3.20.3

[vivekpatani]

I think it's to produce reproducible builds by pinning protoc generation to a specific version.

Source

if [[ $(protoc --version | cut -f2 -d' ') != "3.20.3" ]]; then
  echo "could not find protoc 3.20.3, is it installed + in PATH?"
  exit 255
fi

[moficodes]

Thats reasonable. But the contributing.md does not mention protoc being a requirement. So when make verify is run it will fail the test.

[jmhbnz]

Thanks for raising this @moficodes - I think it makes sense to add a bullet point under https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#option-1---manually-setup-local-environment to cover installing the projects pinned version of protoc. If you have time please raise a pr 🙏🏻

[moficodes]

Please assign this to me.

There is also some other requirements for this that I can add to the same pr.

e.g - yamllint

[serathius]

Would be great enhancement to add a make install-protoc install-yamllint commands