Add documentation/lua-docs

[BuckarooBanzay]

Add documentation for:

• [ ] tp-tube (modding-api and ingame-api)
• [ ] tag-tube (#107)
• [ ] embedded tube registration (modding-api)
• [ ] lua-tube events and interface (ingame)
• [ ] detector tubes (ingame)
• [ ] digiline injector (ingame)

(maybe in a api.md or in the repo readme itself)

[SwissalpS]

+1 for api.md

[S-S-X]

• link #41