Install doc - finding pub

[stas00]

Hi,

I installed dart following the instructions from your linux link https://www.dartlang.org/install/linux, and then:

$ pub global activate linkcheck Command 'pub' not found

Checking the dart .deb package, it puts its bins under /usr/lib/dart/bin/ which is of course is not in my PATH, so it might be useful to add a note helping the user to find pub.

Thanks.