feat(#2): Add a Desktop Entry

This allows it to show in application start menus. It doesn't have
icons yet but will handle in a future commit.

zen.desktop

@@ -0,0 +1,25 @@
+[Desktop Entry]
+Name=Zen Browser
+Exec=zen %u
+Icon=zen
+Type=Application
+MimeType=text/html;text/xml;application/xhtml+xml;x-scheme-handler/http;x-scheme-handler/https;application/x-xpinstall;application/pdf;application/json;
+StartupWMClass=zen-alpha
+Categories=Network;WebBrowser;
+StartupNotify=true
+Terminal=false
+X-MultipleArgs=false
+Keywords=Internet;WWW;Browser;Web;Explorer;
+Actions=new-window;new-private-window;profilemanager;
+
+[Desktop Action new-window]
+Name=Open a New Window
+Exec=zen %u
+
+[Desktop Action new-private-window]
+Name=Open a New Private Window
+Exec=zen --private-window %u
+
+[Desktop Action profilemanager]
+Name=Open the Profile Manager
+Exec=zen --ProfileManager %u