docs: improved operations page

docs/operations.rst

@@ -5,7 +5,16 @@ Operations
 Sometimes more sophisticated filtering operations
 are needed such as getting items that are greater
 than, less than etc. by specific field. For such
-purpose, Red Bird provide operations.
+purpose, Red Bird provide operations:
+
+- ``greater_than``
+- ``less_than``
+- ``not_equal``
+- ``between``
+- ``in_``
+
+Examples
+--------
 
 .. code-block:: python
 
@@ -15,4 +24,12 @@ purpose, Red Bird provide operations.
 
     repo.filter_by(age=less_than(30))
 
-    repo.filter_by(age=not_equal(30))
+    repo.filter_by(age=not_equal(30))
+
+.. code-block:: python
+
+    from redbird.oper import between, in_
+
+    repo.filter_by(age=between(20, 40))
+
+    repo.filter_by(age=in_([20, 40]))