Add *bool-cast*

Author: arielb1

text/0401-coercions.md

@@ -326,6 +326,7 @@ following holds:
 * `e` has type `usize` and `U` is `*U_0`, while `U_0: Sized`; *addr-ptr-cast*
 * `e` has type `T` and `T` and `U` are any numeric types; *numeric-cast*
 * `e` is a C-like enum and `U` is an integer type or `bool`; *enum-cast*
+* `e` has type `bool` and `U` is an integer type or `bool`; *bool-cast*
 * `e` has type `u8` and `U` is `char`; *char-cast*
 * `e` has type `&.T` and `U` is `*T`, and `e` is a mutable reference
    if `U` is. *ref-ptr-cast*