Clarify the description for `umount -a`
Clarify the description for `umount -a`

slash3b/tldr,kuanyui/tldr,kuanyui/tldr,cptdeka10/tldr,WANG-lp/tldr,cdminigun/tldr,WANG-lp/tldr,UncommonPleb/tldr,cdminigun/tldr,AgamAgarwal/tldr,davidsiefert/tldr,ostera/tldr,cptdeka10/tldr,ostera/tldr,Parth-Mehrotra/tldr,mshmoustafa/tldr,cptdeka10/tldr,WALL-E/tldr,danieldiekmeier/tldr,deekim/tldr,danieldiekmeier/tldr,rubenvereecken/tldr,slash3b/tldr,deekim/tldr,Phizho/tldr,lord63-forks/tldr,felixonmars/tldr,katekyan/tldr,mshmoustafa/tldr,felixonmars/tldr,ArturSkowronski/tldr,rubenvereecken/tldr,Phizho/tldr,igorshubovych/tldr,UncommonPleb/tldr,slash3b/tldr,jeremyruppel/tldr,ArturSkowronski/tldr,Qtrain/tldr,deekim/tldr,e0i/tldr,Phizho/tldr,e0i/tldr,NegaMorgan/tldr,zoisom/tldr,Qtrain/tldr,felixonmars/tldr,zoisom/tldr,davidsiefert/tldr,NegaMorgan/tldr,bradparks/tldr,jeremyruppel/tldr,igorshubovych/tldr,bradparks/tldr,katekyan/tldr,zoisom/tldr,lord63-forks/tldr,UncommonPleb/tldr,WALL-E/tldr,katekyan/tldr,AgamAgarwal/tldr,Parth-Mehrotra/tldr