add animation gifs for new rack-mount systems, also update rbuild and the main readme to reflect these changes

rack-mount/tray/README.md

@@ -0,0 +1,9 @@
+# Tray Mounting System
+
+![demo](./animate.gif)
+
+Please see [entry.scad](./entry.scad) for config and building. Make sure the correct rack profile is configured in [rackFrame.scad](../../config/rackFrame.scad).
+
+- Mount on front rails. 
+- Single Part, can also be printed without supports.
+- Includes support for custom bottom screws (`mountPoints` in config). This is useful for SBCs and mini PCs with bottom screws.

rack-mount/tray/animate.scad

@@ -16,5 +16,5 @@ module animateTraySystem(at=$t) {
   dx = abs(lerp(a=-40, b=40, t=at));
   dy = abs(lerp(a=-30, b=30, t=at));
 
-  traySystem(trayU=trayU, baseWidth=x+dx, baseDepth=y+dy, mountPoints=[]);
+  traySystem(trayU=trayU, baseWidth=x+dx, baseDepth=y+dy, mountPoints=[], backLipHeight=8);
 }