Add v4 migration guide for PSR-11

Author: michaelmoussa

docs/book/migration-v4.md

@@ -0,0 +1,36 @@
+# Migration Guide
+
+Migration guide for Zend Service version 4.0.0.
+
+## PSR-11: Container Interface
+
+[`container-interop/container-interop`](https://github.com/container-interop/container-interop)
+was officially deprecated in favor of [PSR-11](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-11-container.md)
+on February 13, 2017. As such, all uses of the `Interop\Container\*` interfaces
+have been replaced with `Psr\Container\ContainerInterface`. Further, installs of
+`container-interop/container-interop` below version `1.2.0` is prohibited via
+Composer's `conflicts` configuration. Version `1.2.0` _does_ extend the PSR-11
+interfaces, and is thus still usable.
+
+If your project typehints any `Interop\ContainerInterop\*` interfaces where any
+`Zend\ServiceManager\*` classes are expected, you _**must**_ update your code to
+expect `Zend\ServiceManager\*` or `Psr\Container\*` classes or interfaces instead.
+The latter is preferred, unless your code utilizes any additional functionality
+provided by the `Zend\ServiceManager\*` classes that are not declared in the
+PSR-11 interfaces.
+
+To do this, use your favorite find-and-replace tool to update the following:
+  - `use Interop\Container\ContainerInterface;` -> `use Psr\Container\ContainerInterface;`
+  - `use Interop\Container\ContainerException;` -> `use Psr\Container\ContainerExceptionInterface;`
+    - **Note:** You will also need to replace `ContainerException` with `ContainerExceptionInterface`
+      where it is used throughout your code. If you _don't_ want to do that, you can include
+      ` as ContainerException` in the find-and-replace, and any existing use of `ContainerException`
+      will continue to work.
+
+> ### Note
+>
+> If you use fully-qualified class names in your typehints, rather than taking
+> advantage of `use` statements, you will need to run additional find-and-replace
+> commands to update those class paths within your code. The exact finds and
+> replaces to run for those scenarios are not covered in this migration guide, as
+> they can vary greatly and are not a generally recommended practice.