What is the problem you're trying to solve

The current documentation on building the development environment describes how to install protoc, but leaves out the following details:

• Additional protocol buffer dependencies must be added to /usr/local/include/ (Ex. google/rpc/status.proto)
• For protocol buffer generation to succeed, the containerd project must be under the GOPATH as Go modules are not accounted for as stated here.

Describe the solution you'd like

The above details should be documented in BULDING.md. The protocol buffer setup script (script/setup/install-protobuf) can also be mentioned, making it faster for new contributors to set up the proper versions of protocol buffer tools and dependencies.

Additional context

No response