Add gradual steering

media/manual.txt

@@ -243,6 +243,9 @@ A few tips for making maps:
   not even being noticed by the player.
 - There is a special "mirror" block that's very useful for creating
   8-symmetrical structures.
+- Add more visual detail only where it's worth it, i.e. where the player will
+  see it, for example the near the start instead of a section that just quickly
+  passed at high speed.
 
 ~~~~~ COMPILING AND MODIFYING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~