weston.ini.man: Clarify what startup-animation means

This isn't about opening new windows but the start-up animation
that desktop-shell does when it is being brought on/started.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

man/weston.ini.man

@@ -422,7 +422,7 @@ sets the effect used when closing windows (string). Can be
 By default, the fade animation is used.
 .TP 7
 .BI "startup-animation=" fade
-sets the effect used for opening new windows (string). Can be
+sets the effect used by desktop-shell when starting up (string). Can be
 .B fade,
 .B none.
 By default, the fade animation is used.