Update linux.md

Improve installation instructions

docs/build-instructions/linux.md

@@ -27,13 +27,17 @@ Ubuntu LTS 12.04 64-bit is the recommended platform.
 
 ## Instructions
 
+If you have problems with permissions don't forget to prefix with `sudo`
+
   ```sh
   git clone https://github.com/atom/atom
   cd atom
   script/build # Creates application at $TMPDIR/atom-build/Atom
   sudo script/grunt install # Installs command to /usr/local/bin/atom
-  script/grunt mkdeb # Generates a .deb package at $TMPDIR/atom-build
+  script/grunt mkdeb # Generates a .deb package at $TMPDIR/atom-build, i.e. /tmp/atom-build
   ```
+  
+To run `atom` and `apm` from a terminal open atom's command pallete `ctrl+shift+p` and run `Window: Install Shell Commands`
 
 ## Troubleshooting