Update CONTRIBUTING.rst
Thanks for the changed. I noticed we did not have qiskit-ignis dependent. This is now required by Aqua for the HHL algorithm.
@@ -177,7 +177,8 @@ correctly achieved by first uninstalling them from the Python environment in whi
have Qiskit (if they were previously installed),
using the ``pip uninstall`` command for each of them. Next, clone the
`Qiskit Terra <https://github.com/Qiskit/qiskit-terra>`__, `Qiskit Aer <https://github.com/Qiskit/qiskit-aer>`__,
-`Qiskit IBMQ Provider <https://github.com/Qiskit/qiskit-ibmq-provider>`__ and
+`Qiskit IBMQ Provider <https://github.com/Qiskit/qiskit-ibmq-provider>`__,
+`Qiskit Ignis <https://github.com/Qiskit/qiskit-ignis>`__ and
`Qiskit Aqua <https://github.com/Qiskit/qiskit-aqua>`__ repositories and
install them in this order from source in the same Python environment.
Qiskit Terra, Qiskit IBMQ Provider and Qiskit Aqua can be installed by issuing the following commands
