DOC: document new filter function

src/doc/tutorials/complex_data_models.rst

@@ -78,7 +78,7 @@ Examples
 
 
 Finding parents and properties
---------
+------------------------------
 To find a specific parent or property of an Entity, its
 ParentList or PropertyList can be filtered using names, ids, or
 entities. A short example:
@@ -126,3 +126,19 @@ entities. A short example:
    # Result: [p2_1]
 
 The filter function of ParentList works analogously.
+
+Finding entities in a Container
+-------------------------------
+In the same way as described above, Container can be filtered.
+A short example:
+
+.. code-block:: python3
+
+   import linkahead as db
+
+   # Setup a record with six properties
+   p1 = db.Property(id=101, name="Property 1")
+   p2 = db.Property(name="Property 2")
+   c = db.Container().extend([p1,p2])
+   c.filter(name="Property 1")
+   # Result: [p1]