[DOC] Add documentation about the project structure (#31)

[alexslkgit]

Description:

It should be done after #31

Link to documentation

The point is to create as good documentation as we can: for all the new joiners.

It should also be as simple as possible. No unnecessary information, just the point. If it's possible o describe it in one sentence - do it!

Also, you can add images, presentation slides, links, memes etc :)

Acceptance criteria:

• We have all the information from #31 us documented
• The home page of documentation is updated also

Notes:

[Hyper-ON3]

https://github.com/skylab-main/ios/wiki/Xcode-Schemes

[tk4chenko]

Дуже круто 🔥🔥🔥