Update Linux installation instructions in README.md
Update Linux installation instructions in README.md

Resolves #2956.

ardeshirj/atom,liuderchi/atom,stinsonga/atom,PKRoma/atom,atom/atom,Mokolea/atom,andrewleverette/atom,t9md/atom,PKRoma/atom,atom/atom,liuderchi/atom,liuderchi/atom,Mokolea/atom,t9md/atom,Arcanemagus/atom,liuderchi/atom,t9md/atom,PKRoma/atom,andrewleverette/atom,andrewleverette/atom,brettle/atom,brettle/atom,stinsonga/atom,ardeshirj/atom,Arcanemagus/atom,brettle/atom,stinsonga/atom,Arcanemagus/atom,ardeshirj/atom,stinsonga/atom,atom/atom,Mokolea/atom