Document pre-Rust-2021 special case for IntoIterator method lookup

This is the #[rustc_skip_array_during_method_dispatch] special case.

Author: mattheww

src/expressions/method-call-expr.md

@@ -66,6 +66,11 @@ Once a method is looked up, if it can't be called for one (or more) of those rea
 If a step is reached where there is more than one possible method, such as where generic methods or traits are considered the same, then it is a compiler error.
 These cases require a [disambiguating function call syntax] for method and function invocation.
 
+> **Edition Differences**: Before the 2021 edition, during the search for visible methods, if the candidate receiver type is an [array type], methods provided by the standard library [`IntoIterator`] trait are ignored.
+>
+> The edition used for this purpose is determined by the token representing the method name.
+
+
 <div class="warning">
 
 ***Warning:*** For [trait objects], if there is an inherent method of the same name as a trait method, it will give a compiler error when trying to call the method in a method call expression.
@@ -79,9 +84,11 @@ Just don't define inherent methods on trait objects with the same name as a trai
 [_Expression_]: ../expressions.md
 [_PathExprSegment_]: ../paths.md#paths-in-expressions
 [visible]: ../visibility-and-privacy.md
+[array type]: ../types/array.md
 [trait objects]: ../types/trait-object.md
 [disambiguate call]: call-expr.md#disambiguating-function-calls
 [disambiguating function call syntax]: call-expr.md#disambiguating-function-calls
 [dereference]: operator-expr.md#the-dereference-operator
 [methods]: ../items/associated-items.md#methods
 [unsized coercion]: ../type-coercions.md#unsized-coercions
+[`IntoIterator`]: ../../std/iter/trait.IntoIterator.html