Added a note about BC (#111)

Added a section about BC

Author: Nyholm

httplug/backwards-compatibility.rst

@@ -0,0 +1,30 @@
+Backwards compatibility
+=======================
+
+Backwards compatibility is an important topic for us, as it should be in every open source project. We follow
+Semver_ which allows us to only break backwards compatibility between major versions. We use
+deprecation notices to inform you about the changes made before they are removed.
+
+Our backwards compatibility promise does not include classes or functions with the ``@internal`` annotation.
+
+Symfony Bundle
+--------------
+
+The HttplugBundle is just a Symfony integration for HTTPlug and it does not have any classes which falls under the BC
+promise. The backwards compatibility of the bundle is only the configuration and its values (and of course the behavior
+of those values).
+
+Discovery
+---------
+
+The order of the strategies is not part of our BC promise. The strategies themselves are marked
+as ``@internal`` so they are also not part of our BC promise.
+However, we do promise that we will not remove a strategy neither will we remove classes from the
+``CommonClassesStrategy``. We will also support the following Puli versions:
+* 1.0.0-beta9
+* 1.0.0-beta10
+
+The consequences of the BC promise for the discovery library is that you can not rely on the *same* client to be
+returned in the future. However, if discovery does find a client now, you can be sure that after future updates it will still discover a client.
+
+.. _Semver: http://semver.org/

index.rst

@@ -74,6 +74,8 @@ for discussion around a future HTTP client PSR.
 
    integrations/index
 
+   Backwards compatibility <httplug/backwards-compatibility>
+
 .. toctree::
    :hidden:
    :caption: Components