Draft to add scalanative doc

[c0d33ngr]

This is a draft for a checklist item of issue #3647

[c0d33ngr]

Hi @lihaoyi something like this or I have to use scalatags and mainargs?

[lihaoyi]

Let's use the same scalatags/mainargs example as we did in scalalib/basic/1-simple/.

You can get rid of most of the docs that are already part of scalalib/basic/1-simple/. The point of this page is to show what's unique about scala native, so the docs should highlight the differences and unique features of it: e.g. the compile to binary, the different optimization levels, etc.

[c0d33ngr]

Alright, it's noted