Update readme for Ubuntu and Debian

Author: khurshid-alam

README.md

@@ -18,7 +18,7 @@ First, you need to compile the theme using the [Sass](http://sass-lang.com/) com
 
 To install Sass, install Ruby and the gem command using your distribution's package manager. Then install `sass` with the `gem` command,
 
-`gem install sass`
+`gem install sass` (not needed for Ubuntu/Debian)
 
 You'll also need the ```glib-compile-schemas``` and  ```gdk-pixbuf-pixdata``` commands in your path to generate the gresource binary. Install them using your distribution's package manager.
 
@@ -27,7 +27,7 @@ You'll also need the ```glib-compile-schemas``` and  ```gdk-pixbuf-pixdata``` co
 |![arch][arch]  ![antergos][antergos]|`sudo pacman -S glib2 gdk-pixbuf2`|
 |![opensuse][opensuse]|`sudo zipper install glib2-devel gdk-pixbuf-devel`|
 |![fedora][fedora]|`sudo dnf install glib2-devel gdk-pixbuf2-devel`|
-|![debian][debian]  ![ubuntu][ubuntu]|`sudo apt-get install libglib2.0-dev libgdk-pixbuf2.0-dev libxml2-utils`|
+|![debian][debian]  ![ubuntu][ubuntu]|`sudo apt-get install ruby-sass libglib2.0-dev libgdk-pixbuf2.0-dev libxml2-utils`|
 
 After installing all the dependencies, change to the cloned directory and, run the following in Terminal,