fix docstrings

pennylane/registers.py

@@ -37,11 +37,22 @@ def registers(register_dict):
 
  **Example**
 
- >>> wire_registers = qml.registers({"alice": 1, "bob": {"nest1": 2, "nest2": 1}})
+ Given input ``{"ancilla": {"sub_ancilla": 2, "sub_ancilla1": 1}}``, ``qml.registers()`` creates
+ a dictionary with 3 key-value pairs. The keys are the register names found in the input:
+ "ancilla", "sub_ancilla" and "sub_ancilla1". The values are the respective :class:`~.Wires`
+ objects for each register. For example, "ancilla" has two sub registers "sub_ancilla" and
+ "sub_ancilla1". Therefore, the value associated with key "ancilla" is the union of the
+ :class:`~.Wires` of its sub registers. Since its sub registers "sub_ancilla" and "sub_ancilla1"
+ have :class:`~.Wires` objects ``Wires([0, 1])`` and ``Wires([2])`` respectively, the key "ancilla"
+ has the value ``Wires([0, 1, 2])``.
+
+ >>> wire_registers = qml.registers({"ancilla": {"sub_ancilla": 2, "sub_ancilla1": 1}})
  >>> wire_dict
- {'alice': Wires([0]), 'nest1': Wires([1, 2]), 'nest2': Wires([3]), 'bob': Wires([1, 2, 3])}
- >>> wire_dict['nest1']
- Wires([1, 2])
+ {'sub_ancilla': Wires([0, 1]), 'sub_ancilla1': Wires([2]), 'ancilla': Wires([0, 1, 2])}
+ >>> wire_dict['sub_ancilla1']
+ Wires([2])
+ >>> wire_dict['sub_ancilla'][1]
+ 1
 
  A simple example showcasing how to implement the `SWAP <https://en.wikipedia.org/wiki/Swap_test>`_ test: