doc(runtime) Add script to automate the build and installation of a custom shared library

[Ivan Enderlin]

Motivation

For the moment, wasmer-go comes with precompiled shared library objects. If the user needs a specific one, it's possible to build and install a custom one by hand. However, having a script to automate that process would be much more comfortable for the user.

Proposed solution

Use the justfile to achieve that.