update the clone step in the installation guide to include submodules

[agarwalrounak]

Details

When running the pre-commit command pre-commit run, it gives the error that .pre-commit-config.yaml does not exist though the command ls -a clearly mentions that .pre-commit-config.yaml exists.

Actual Result

[stsewd]

You are missing the submodule.

git submodule update --init

We should update the clone step in the installation guide to include submodules.

https://docs.readthedocs.io/en/stable/install.html#get-and-run-read-the-docs

[agarwalrounak]

@stsewd Thanks for the prompt reply :) I will send a PR with the required changes soon.