Improve local testing docs

[alessfg]

Is your feature request related to a problem? Please describe

Users should have a clear and concise step by step guide detailing how to locally test any changes made to an image.

Describe the solution you'd like

A clear and concise step by step guide detailing how to locally test any changes made to an image.

Describe alternatives you've considered

N/A

Additional context

PRs should always be tested before submission; but if we don't provide users an easy way to test PRs, they are unlikely to go out of their way to test the code.