Add docs to main.rs for plastic tui.

[Amjad50]

I really don't see a point of the comments here, they just explain the code and its clear enough when reading the code

[silverhadch]

Well yeah, I think ui.rs needs them instead of main.rs. But congrats, you wrote self-explanatory code (in contrast to me when I wrote school software for 2 years and small commits changed 30 files, where I had to drop comments everywhere so my future self knew what the hell past me was doing, lol).