Link to “Getting Started” / README.md

First of all, thank you for such a nice project!

Trying a-shell for the first time, I struggled to use `clang` correctly. The website for the app (i.e. this repo), just lists all the features but not how to use them. (At least that’s my impression.)

A simple remedy would be to link to the main repo’s [README](https://github.com/holzschu/a-shell).

Update README.md to include a link to the main a-Shell repository's README, especially its Getting Started guidance. Check the existing README.md presentation first, then verify that the link is visible and opens the intended repository documentation.

Scritto dal modello di indicizzazione a partire dal testo della issue.