Add priority order explanation for tagged services

Hi,

In this page, the priority order is not explained for tagged services. Since I needed to know this, I guess it is a good addition.
The text is mostly inspired from the paragraph about priority in the event dispatcher documentation : https://symfony.com/doc/current/event_dispatcher.html#creating-an-event-listener 

Fell free to edit it or to provide me some advice to do it.

Regards

Author: hermann8u

service_container/tags.rst

@@ -595,6 +595,9 @@ Tagged Services with Priority
 The tagged services can be prioritized using the ``priority`` attribute,
 thus providing a way to inject a sorted collection of services:
 
+.. tip::
+The priority is a positive or negative integer. The higher the number, the earlier the tagged service will be located in the collection.
+
 .. configuration-block::
 
     .. code-block:: yaml