Add MacOS instructions for modifying `sudoers`

[bgyarfas]

It could be helpful for MacOS users if there was a note about needing to adjust the sudoers file by using sudo visudo and adding the following line:

<USER>        ALL = (root) NOPASSWD: <PATH_TO_AUSTIN>

(With the appropriate substitutions).

Thanks for the great work!

[P403n1x87]

@bgyarfas thanks for the feedback. I'll add more instructions in future releases of the extension, but feel free to contribute as well! 🙂