Update installation instruction on Debian systems

[utkarsh2102]

Hi @zyedidia,

Now since we have micro available on apt, it'd make more sense to use that, instead of snap :)
Let me know if this needs further editing.

[zyedidia]

This is roughly the same as #1506. To make sure I understand correctly, micro is only available via apt on Ubuntu 20.04 which has not been released yet, so for most people this won't work yet. Please correct me if I'm wrong. I think #1506 addresses my concerns on that front.

I think it's also best to keep the instructions for installing via snap, since that it still a useful method.

[rajudev]

Looks like I created #1506 without looking at the existing PR's.
The only difference is that I added a badge there.

Should I close #1506 ?