docs(ngRepeat): add info about aliasing special properties of ngRepeat

This will safe peoples' time, since ngRepeat's docs, not ngInit's, is the first
place where one would search for such info.

Closes angular#5622

Author: vucalur

src/ng/directive/ngRepeat.js

@@ -20,6 +20,8 @@
  * | `$even`   | {@type boolean} | true if the iterator position `$index` is even (otherwise false).           |
  * | `$odd`    | {@type boolean} | true if the iterator position `$index` is odd (otherwise false).            |
  *
+ * Creating aliases for these properties is possible with {@link api/ng.directive:ngInit `ngInit`}.
+ * This may be useful when, for instance, nesting ngRepeats.
  *
  * # Special repeat start and end points
  * To repeat a series of elements instead of just one parent element, ngRepeat (as well as other ng directives) supports extending