[Doc]: Update doc for "Set up the Documentation"

[lee1043]

Describe your documentation update

During the Step 3 from README.rst, step for updating docs/conf.py needs to be added to avoid the following issue.

>>> make docs

rm -rf docs/generated
cd docs && make html
Running Sphinx v5.3.0

Configuration error:
There is a programmable error in your configuration file:

Traceback (most recent call last):
  File "/Users/lee1043/mambaforge/envs/pcmdi_utils_dev/lib/python3.10/site-packages/sphinx/config.py", line 350, in eval_config_file
    exec(code, namespace)
  File "/Users/lee1043/Documents/Research/git/pcmdi_utils/docs/conf.py", line 24, in <module>
    import python_template
ModuleNotFoundError: No module named 'python_template'

make[1]: *** [html] Error 2
make: *** [docs] Error 2

[lee1043]

@tomvothecoder I made a quick fix for this but repo does not allow me to create a PR. I'd be happy to provide the minor updated code via email or PR if you are okay with granting me permission.

$ git push -u origin lee1043-patch-1

ERROR: Permission to tomvothecoder/python-template-repo.git denied to lee1043.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

[tomvothecoder]

@lee1043 Thanks for trying out this repo. I added you as a collaborator so you should be able to create a branch directly on the repo now.