fix(readme): add warning in docs/README.rst

Author: nb

docs/README.rst

@@ -16,6 +16,25 @@ php-formula
 
 Formula to set up and configure php
 
+.. list-table::
+   :name: banner-breaking-changes-v1.0.0
+   :header-rows: 1
+   :widths: 1
+
+   * - WARNING: BREAKING CHANGES FOR UPCOMING ``v1.0.0``
+   * - This formula currently provides two methods for managing PHP; the old method
+       under `php` and the new method under `php.ng`. In upcoming `v1.0.0`, the old
+       method will be removed and `php.ng` will be promoted to `php` in its place.
+
+       If you are not in a position to migrate, you will need to pin your repo to
+       the final release tag before `v1.0.0`, which is expected to be `v0.37.1`.
+
+       If you are currently using `php.ng`, there is nothing to do until `v1.0.0`
+       is released.
+
+       To migrate from the old `php`, the first step is to convert to `php.ng`,
+       before `v1.0.0` is released.
+
 .. contents:: **Table of Contents**
 
 General notes