more docs.

src/math/Spherical.js

@@ -4,6 +4,9 @@
  *
  * Ref: https://en.wikipedia.org/wiki/Spherical_coordinate_system
  *
+ * The poles (phi) are at the positive and negative y axis.
+ * The equator starts at positive z.
+ *
  */
 
 THREE.Spherical = function ( radius, phi, theta ) {