docs(ngRepeat): clarify 'as' microsyntax usage

Closes angular#11087

Author: Artem

src/ng/directive/ngRepeat.js

@@ -144,6 +144,11 @@
  *     For example: `item in items | filter:x as results` will store the fragment of the repeated items as `results`, but only after
  *     the items have been processed through the filter.
  *
+ *     Please note that `as [variable name] is not an operator but rather a part of ngRepeat micro-syntax so it can be used only at the end
+ *     (and not as operator, inside an expression).
+ *
+ *     For example: `item in items | filter : x | orderBy : order | limitTo : limit as results` .
+ *
  * @example
  * This example initializes the scope to a list of names and
  * then uses `ngRepeat` to display every person: