Allow using the pipe command to send screen and scrollback contents directly to the clipboard

See #1693

docs/changelog.rst

@@ -29,6 +29,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
   option to have the kitten wait till copying to clipboard is complete
   (:iss:`1693`)
 
+- Allow using the :doc:`pipe <pipe>` command to send screen and scrollback
+  contents directly to the clipboard (:iss:`1693`)
+
 - Linux: Disable the Wayland backend on GNOME by default as GNOME has no
   support for server side decorations. Can be controlled by
   :opt:`linux_display_server`.

docs/pipe.rst

@@ -43,6 +43,10 @@ You can choose where to run the pipe program:
 ``tab``
    A new window in a new tab
 
+``clipboard, primary``
+   Copy the text directly to the clipboard. In this case the specified program
+   is not run, so use some dummy program name for it.
+
 ``none``
    Run it in the background