Fixed readthedoc failed build.
Created by: DamonLee5
Currently, the readthedoc of mbircone are fail to build.
The reason is that NumPy 1.22.0 does not support Python 3.7(Default Readthedoc Python) anymore. The solution is to add a readthedoc configuration file to ask readthedoc to use python 3.9 to build the documentation.
I tested this thing on my fork. It builds successfully. https://readthedocs.org/projects/mbircone-wenrui/builds/.