added a note about PRs being merged automatically

Author: fabpot

README.rst

@@ -15,6 +15,24 @@ project, run the following command:
 For more information about contributing a recipe, read the `documentation`_ on
 the main repository.
 
+Unlike for official recipes, the pull requests for new contrib recipes are
+managed by the community. Pull requests are reviewed by the Symfony Bot and
+automatically merged when the following conditions are met (in that order):
+
+* The pull request title does not contain "WIP";
+
+* The Symfony Bot approved the pull request and reported no validation errors;
+
+* Someone (not the Symfony bot nor the pull request author) approved the pull
+  request;
+
+* The pull request author or the reviewer is a "trusted user". A "trusted user"
+  being one of the following:
+
+  * A Symfony Core Merger;
+
+  * A user part of a Github team for all modified/deleted/added packages.
+
 .. _`Symfony Flex`: https://github.com/symfony/flex
 .. _`Symfony recipes`: https://github.com/symfony/recipes
 .. _`documentation`: https://github.com/symfony/recipes