Adds pre-commit hooks for black, flake8, isort

[chrismoradi]

Description

This PR fixes #194

Ran into this issue with new install of black, but the pre-commit hook should be correct.

Questions for reviewer:

• Is there somewhere I should add documentation on installing and running pre-commit hooks (e.g., README.md or CONTRIBUTING.md)?
• Do you use the default line length with black? Any other settings that should be specified for other hooks?

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[sansyrox]

Hi @chrismoradi ,

Thank you for the contribution 😄

I have a few suggestions:

• Can you set the default_stage(https://pre-commit.com/#top_level-default_stages) to push?
• I use max line length of 160 in flake8 (https://github.com/sansyrox/robyn/blob/main/.flake8)
• We do have a CONTRIBUTORS.MD file but it is a little generic at the moment. Can you add the install instructions in README for now?
  This section(https://github.com/sansyrox/robyn#%EF%B8%8F-to-develop-locally) should work.

[chrismoradi]

@sansyrox, I added the default_stage and install instructions to the README (please let me know if you want me to rework that).

For flake8, it looks like it's using the config settings already in .flake8. I tested changing the max line length to 90 and it starts showing line length errors. Happy to add this to the pre-commit config but thought it would add extra maintenance to have this setting in 2 places.

Also added a config line for black to use 160 max line length.

[sansyrox]

LGTM! 🚀

Thank you so much!