README.md: Mention lazy_init.

README.md

@@ -3,12 +3,16 @@
 The classes in this library make it easier to enforce envariants in larger classes.
 None of them serve a business need directly, but they all make it easier to write classes that do.
 
-## `propagate_const`
+## `propagate_const<PointerType>`
 
 Ensures that a const pointer also points to a const object.
 
 This type has been suggested as an addition to C++'s standard library. (Proposal [N4388](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4388.html))
 
-## `not_null`
+## `not_null<PointerType>`
 
-Ensures that a pointer can never be null.
+Ensures that a pointer can never be null.
+
+## `lazy_init<T>`
+
+Ensures that the wrapped data is initialized exactly once, in a thread- and exception safe manner.