docs(pipes): change description for parameters to reflect change in beta.16

closes #1197

Author: teropa

public/docs/ts/latest/guide/pipes.jade

@@ -125,9 +125,10 @@ figure.image-display
   * A pipe is a class decorated with pipe metadata.
 
   * The pipe class implements the `PipeTransform` interface's `transform` method that
-  accepts an input value and an optional array of parameters and returns the transformed value.
+  accepts an input value followed by optional parameters and returns the transformed value.
 
-  * There will be one item in the parameter array for each parameter passed to the pipe
+  * There will be one additional argument to the `transform` method for each parameter passed to the pipe.
+  Our pipe has one such parameter: The `exponent`.
 
   * We tell Angular that this is a pipe by applying the
   `@Pipe` decorator which we import from the core Angular library.