Adds note on new validation files scanned in 2.7

Author: GromNaN

book/validation.rst

@@ -103,6 +103,11 @@ following:
     Protected and private properties can also be validated, as well as "getter"
     methods (see :ref:`validator-constraint-targets`).
 
+.. versionadded:: 2.7
+    Since 2.7, XML and YAML constraint files located in the `Resource/config/validation/`
+    sub-directory of a bundle are loaded. Previously, only `Resource/config/validation.xml`
+    and `Resource/config/validation.yml` were allowed to register contraints.
+
 .. index::
    single: Validation; Using the validator