Update effective-lexing.md to more clearly callout the lexing API (#240)

I coerced some of my students into trying out parsley. They seem to like
it in general, but they missed the existence of the lexing API, and
spend some time implementing their own lexer.

This tries to make the callout in the beginning more “in your face”.

docs/tutorial/effective-lexing.md

@@ -5,9 +5,9 @@ laika.site.metadata.description = "How to handle low-level tokenisation in a par
 # Effective Lexing
 
 @:callout(info)
-Note that the start of this page describes the underlying fundamentals behind
-lexing with parser combinators, but this is abstracted by the functionality
-at the end.
+Parsley offers a user-friendly API for lexing, which is detailed at the end of this document. We recommend using this API for most purposes.
+
+The initial sections of this document explain the fundamental principles behind lexing with parser combinators.
 @:@
 
 In the previous post, we saw the basic principles behind handling whitespace in a transparent manner.