Add pre-commit hooks

[bhishanpdl]

Add pre-commit hooks for debug-statements and so on.
Make sure you do not accidentally commit wrong commits.

Reference: https://github.com/pre-commit/pre-commit-hooks

Using pre-commit:

pip install pre-commit
cd to_your_repo
pre-commit --version
make sure you have .pre-commit-config.yaml file at the root of the repo

pre-commit install # this will create `.git/hooks/pre-commit` executable file

Deliberately I have a file tests/tests_example.py which should fail.

pre-commit run --all-files # gives fail error.

Once the pre-commit command is run in GitHub repo, usual git commands will use the git hooks automatically. This means whenever we run git commit -m "hello" the command will fail if it does not meet the requirements.