Tweak mac Atom install instructions to reference extracting the .zip

Author: tjgrathwell

sites/en/installfest/_install_atom_for_mac.step

@@ -10,12 +10,12 @@ step "Download Atom" do
   message "Download the [Atom installer](https://atom.io/download/mac)."
 end
 
-step 'Save the file to your desktop, if prompted, or go to the Downloads folder' do
-  message "Auto-saved, without a prompt, to downloads should be the default."
+step 'Find the downloaded file in Finder' do
+  message "If you weren't asked where to save it, it's probably in the Downloads folder."
 end
 
-step "Drag Atom into your Applications folder." do
-  message "From your save location (default is Downloads). Drag Atom into your Applications folder."
+step "Extract Atom and move it to your Applications folder." do
+  message "Double click the Atom `.zip` file to extract it. Drag Atom into your Applications folder."
 
-  img src: 'img/install_atom_mac.gif', alt: 'Contents of the downloaded file'
+  img src: 'img/install_atom_mac.gif', alt: 'Animation of extracting the Atom zip file and moving the contents to the Applications folder'
 end