Session files: Expand environment variables

docs/overview.rst

@@ -173,6 +173,11 @@ option in :file:`kitty.conf`. An example, showing all available commands:
     The :doc:`launch <launch>` command when used in a session file cannot create
     new OS windows, or tabs.
 
+.. note::
+   Environment variables of the for :code:`${NAME}` or :code:`$NAME` are
+   expanded in the session file, except in the *arguments* (not options) to the
+   launch command.
+
 
 Creating tabs/windows
 -------------------------------