docs: add comprehensive README for Warnet demo project

[b-l-u-e]

Add a beginner-friendly guide that teaches users how to:

• Set up Warnet using standard installation workflow
• Deploy Bitcoin networks with warnet new command
• Run existing scenarios (miner_std, tx_flood, reconnaissance)
• Monitor and interact with networks via dashboard

This provides a simple entry point for new users to learn Warnet without requiring custom scripts or source installation.

[pinheadmz]

This is great work, thank you -- however I was thinking we could offer more resources like in https://github.com/bitcoin-dev-project/battle-of-galen-erso.

What do you think about making this repo a warnet project with a one-tank network (e.g. 94.0.0-5k-inv) and only one scenario (e.g. my_first_attack_5kinv.py). Link to the main warnet docs as much as you can for install and setup and then instruct the user how to monitor their tiny network, execute the attack, and watch its progress.