Allow setting the class for new OS windows in a session file

docs/changelog.rst

@@ -20,6 +20,8 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 
 - Implement support for box drawing rounded-corners characters (:iss:`2240`)
 
+- Allow setting the class for new OS windows in a session file
+
 - When a character from the Unicode Dingbat block is followed by a space, use
   the extra space to render a larger version of the character (:iss:`2850`)
 

docs/index.rst

@@ -346,6 +346,8 @@ For example:
     new_os_window
     # set new window size to 80x25 cells
     os_window_size 80c 25c
+    # set the --class for the new OS window
+    os_window_class mywindow
     launch sh
     # Make the current window the active (focused) window
     focus