Add missing development documentation

[kantord]

• Document where images come from
• Document where sounds come from
• Document previewing courses locally
• Document list of Python packages
• Document setting up Python packages
• Document testing Python packages
• Document Cypress testing
• Document how to write new Gherkin tests

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[jdmaras]

I was trying to work on documenting where the sounds come from but I was hoping for some clarification on what exactly I was doing.

Am I documenting what site created the sound?

[jowodo]

This seems related to these two open issues:

• Import audio data from other free/open-source projects #714
• Sourcing audio from Lingua Libre #1464
  It may be advantageous to document something else, because the sound generation might change and the documentation will need to be rewritten. If I remember correctly, images are similarly stored as sound (at the moment at least). So, writing documentation about how images are handled and pointing out differences to sounds may be something to look into? What do you think?

[kantord]

yes, well, those are future plans for where the sound comes from. I think those should be in the documentation and the issues should be linked, because a lot of people are interested in this topic,

the current sound that exists is fetched by a TTS engine through an API, and that is also very important to be documented

I think the best place to start research could be this closed issue, that is already completed that the pull request where it was fixed is also linked there #1473

let me know if you need more help regarding this or anything