intro: mention banana-gorilla-jungle problem

Author: jll63

doc/introduction.adoc

@@ -9,6 +9,13 @@ the Expression Problem:
 to add new operations on the existing types, and new types to the existing
 operations, without modifying existing code?
 
+Open-methods also address the banana-gorilla-jungle problem:
+
+> The problem with object-oriented languages is they’ve got all this implicit
+environment that they carry around with them. You wanted a banana but what you
+got was a gorilla holding the banana and the entire jungle.  — Joe Armstrong,
+creator of Erlang progamming language
+
 As a bonus, open-methods can take more than one argument into account when
 selecting the appropriate function to call - aka multiple dispatch. For that
 reason, open-methods are often called multi-methods, but that term is