Document window-icon

Signed-off-by: Sebastian Ramacher <sebastian+dev@ramacher.at>

zathurarc.5.rst

@@ -593,6 +593,13 @@ Defines the vertical padding of the statusbar and notificationbar
 * Value type: Integer
 * Default value: 2
 
+window-icon
+^^^^^^^^^^^
+Defines the path for a icon to be used as window icon.
+
+* Value type: String
+* Default value:
+
 window-height
 ^^^^^^^^^^^^^
 Defines the window height on startup