docs(menu): fix and clarify documentation md-offset (angular#9911)

docs(menu): fix and clarify documentation md-offset

Author: derekrliang

src/components/menu/js/menuDirective.js

@@ -97,9 +97,9 @@
  * This offset is provided in the format of `x y` or `n` where `n` will be used
  * in both the `x` and `y` axis.
  *
- * For example, to move a menu by `2px` from the top, we can use:
+ * For example, to move a menu by `2px` down from the top, we can use:
  * <hljs lang="html">
- * <md-menu md-offset="2 0">
+ * <md-menu md-offset="0 2">
  *   <!-- menu-content -->
  * </md-menu>
  * </hljs>