Re-organise README.md

Author: haphan

README.md

@@ -15,12 +15,11 @@ OpenStack services, and versions of services, are supported.
 * [Contributing guide](/CONTRIBUTING.md)
 * [Code of Conduct](/CODE_OF_CONDUCT.md)
 
-## Backward incompatibility
+## Getting help
+   
+- Meet us on Slack: https://phpopencloud.slack.com ([Get your invitation](https://launchpass.com/phpopencloud))
+- Report and issue: https://github.com/php-opencloud/openstack/issues
 
-Due to new [object typehint](https://wiki.php.net/rfc/object-typehint) since PHP 7.2, `Object` is a reserved keyword 
-thus class `OpenStack\ObjectStore\v1\Models\Object` had to be renamed to 
-`OpenStack\ObjectStore\v1\Models\StorageObject`. See [#184](https://github.com/php-opencloud/openstack/pull/184) for 
-details.
 
 ### Version Guidance
 
@@ -29,14 +28,18 @@ details.
 | `^2.0`    | Maintained (Bug fixes only) | `>=7.0,<7.2`  | March 2016 - March 2018 |
 | `^3.0`    | Latest                      | `^7.0`        | March 2018 - March 2020 |
 
-## Getting help
-   
-- Meet us on Slack: https://phpopencloud.slack.com ([Get your invitation](https://launchpass.com/phpopencloud))
-- Report and issue: https://github.com/php-opencloud/openstack/issues
+## Upgrade from 2.x to 3.x
+
+Due to new [object typehint](https://wiki.php.net/rfc/object-typehint) since PHP 7.2, `Object` is a reserved keyword 
+thus class `OpenStack\ObjectStore\v1\Models\Object` had to be renamed to 
+`OpenStack\ObjectStore\v1\Models\StorageObject`. 
+
+This change was introduced in [#184](https://github.com/php-opencloud/openstack/pull/184).
 
 ## Requirements
 
 * PHP 7.0
+* `ext-curl`
 
 ## How to install