add AnimPreload info

panda/src/doc/eggSyntax.txt

@@ -1515,6 +1515,19 @@ GROUPING ENTRIES
     current group, regardless of the group in which the geometry is
     actually defined.  See the <Joint> description, below.
 
+  <AnimPreload> { 
+    <Scalar> fps { float-value }
+    <Scalar> num-frames { integer-value } 
+  }
+
+    One or more AnimPreload entries may appear within the <Group> that
+    contains a <Dart> entry, indicating an animated character (see
+    above).  These AnimPreload entries record the minimal preloaded
+    animation data required in order to support asynchronous animation
+    binding.  These entries are typically generated by the egg-optchar
+    program with the -preload option, and are used by the Actor code
+    when allow-async-bind is True (the default).
+
 
 <Instance> name { group-body }