Add missing MongoDB version check command to setup documentation

[vaibhav45sktech]

While setting up the Databus / Rocket.Chat dev environment, new
contributors may need to verify their MongoDB version to ensure
compatibility.

The current README does not mention how to check the MongoDB version
in Ubuntu, which often leads to confusion during setup.

I propose adding a small troubleshooting tip in the README with the
standard MongoDB version check commands.

[Kgupta62]

Hi 👋

I’d like to work on this issue and add the MongoDB version check instructions to the README for Ubuntu users.
I have 2+ years of industry experience in a product-based company, have contributed to multiple open-source projects, and have hands-on experience working with MongoDB.

Please assign this issue to me so I can start working on it and submit a PR.

Thanks!

[vaibhav45sktech]

@Kgupta62 @shoaibkhan-sde this issue has already been taken care of since i raised this issue with the intent to solve myself . thanks for ur time and contribution.