* Clarify “Building Ruby” docs

* Fix test examples to work from `build` dir

* Clarify “Testing Ruby” examples with real examples

All the commands should run correctly by default, without the user needing to modify them. This builds confidence that the relative paths are working correct from within the `build` directory.

Also, let’s use a consistent example throughout, for greater clarity.

* Improve examples to use `-v` flag in-context

This shows the correct way to combine `-v` with another parameter, e.g. a specific file to test.

* Other readability improvements

* Clarify `make` implementation support