Doc/protobuf build instructions

[thomassedlmayer]

Description

I added the protobuf installation instructions by @pmai (see here) to the build_install_example.adoc. I recently followed these instructions and they worked fine.

Check the checklist

• [x] I have performed a self-review of my own code.
• [x] I have made corresponding changes to the documentation for osi-sensor-model-packaging.
• [x] My changes generate no new warnings.
• [x] I have added tests that prove my fix is effective or that my feature works.
• [ ] New and existing unit tests / Github Actions pass locally with my changes.