Update install-win10.md (#210)

Author: neutronstriker

WSL/install-win10.md

@@ -67,7 +67,7 @@ You're done!  Now you can use your Linux environment.
 
 lxrun installs Ubuntu user-mode by default on top of the Windows Subsystem for Linux.  
 
-> Since moving to the store, we have stopped keeping this user-mode image up to date.  When you're done, run `apt-get update`.
+> Since moving to the store, we have stopped keeping this user-mode image up to date.  When you're done, run `sudo apt-get update` and then `sudo apt-get upgrade`.
 
 1. Turn on Developer Mode