Doc'd that Count("*") is equivalent to COUNT(*) SQL.

docs/ref/models/querysets.txt

@@ -3898,6 +3898,7 @@ by the aggregate.
 .. class:: Count(expression, distinct=False, filter=None, **extra)
 
     Returns the number of objects that are related through the provided
+    expression. ``Count('*')`` is equivalent to the SQL ``COUNT(*)``
     expression.
 
     * Default alias: ``<field>__count``