Add documentation for the env processor

Author: Orkin

configuration/environment_variables.rst

@@ -502,6 +502,9 @@ Symfony provides the following env var processors:
     and end of the string. This is especially useful in combination with the
     ``file`` processor, as it'll remove newlines at the end of a file.
 
+``env(explode:FOO,BAR)``
+    Explode the content of ``FOO,BAR`` env var, retrieving a php array.
+
 ``env(key:FOO:BAR)``
     Retrieves the value associated with the key ``FOO`` from the array whose
     contents are stored in the ``BAR`` env var: