Added a note about cache:clear and cache:pool:clear

Author: javiereguiluz

components/cache/cache_pools.rst

@@ -130,11 +130,16 @@ when all items are successfully deleted)::
     .. code-block:: terminal
 
         $ php bin/console cache:pool:clear <cache-pool-name>
-        
+
         # clears the "cache.app" pool
         $ php bin/console cache:pool:clear cache.app
 
         # clears the "cache.validation" and "cache.app" pool
         $ php bin/console cache:pool:clear cache.validation cache.app
 
+    .. versionadded:: 3.4
+        Starting from Symfony 3.4, the ``cache:clear`` command no longer clears
+        the cache pools, so you must use the ``cache:pool:clear`` command to
+        delete them.
+
 .. _`Doctrine Cache`: https://github.com/doctrine/cache