Add javadoc to Presence.priority

smack-core/src/main/java/org/jivesoftware/smack/packet/Presence.java

@@ -66,7 +66,15 @@ public final class Presence extends Stanza implements TypedCloneable<Presence> {
 
     private Type type = Type.available;
     private String status = null;
+
+    /**
+     * The priority of the presence. The magic value {@link Integer#MIN_VALUE} is used to indicate that the original
+     * presence stanza did not had an explicit priority set. In which case the priority defaults to 0.
+     *
+     * @see <a href="https://tools.ietf.org/html/rfc6121#section-4.7.2.3">RFC 6121 § 4.7.2.3.</a>
+     */
     private int priority = Integer.MIN_VALUE;
+
     private Mode mode = null;
 
     /**