Add to Nest.js docs

[hsluoyz]

Like: https://docs.nestjs.com/security/authorization#integrating-casl

[casbin-bot]

@nodece @Shivansh-yadav13

[Muzzu8421]

Hi, I would like to work on adding Nest.js documentation for Casbin.

I have experience with Node.js and backend frameworks, and I’d love to contribute this.
Could you please guide me on what should be included or assign this to me?

[Muzzu8421]

Hi, I have opened a PR for this issue. Please let me know if any changes are required. Thank you!