Added compatibility notice to readme

Author: KyNorthstar

README.md

@@ -6,3 +6,12 @@ A few ways to have a lazily-initialized value in Swift 5.1. Note that, if you ar
  * [`Lazy`](https://github.com/RougeWare/Swift-Lazy-Patterns/blob/master/Lazy.swift#L184-L248): A non-resettable lazy pattern, to guarantee lazy behavior across Swift language versions
  * [`ResettableLazy`](https://github.com/RougeWare/Swift-Lazy-Patterns/blob/master/Lazy.swift#L252-L330): A resettable lazy pattern, whose value is generated and cached only when first needed, and can be destroyed when no longer needed.
  * [`FunctionalLazy`](https://github.com/RougeWare/Swift-Lazy-Patterns/blob/master/Lazy.swift#L334-L444): An idea about how to approach the lazy pattern by using functions instead of branches.
+
+
+# Compatibility Notice #
+
+The API had notable changes when transitioning from 1.1.0 to 2.0.0. To ease this transition, `Lazy.swift` was left in the root of this repo.
+
+Additionally, to make this a Swift Package, both `Lazy.swift` and its tests were duplicated.
+
+In version 3.0.0, `Lazy.swift` will be moved to `LazyContainers/Sources/LazyContainers/LazyContainers.swift` in order to reduce this duplication. To ease that transition, you should change any hard-coded references to `Lazy.swift` to point to `LazyContainers/Sources/LazyContainers/LazyContainers.swift`.