Document hardware measurement scope

[zhouzhou626]

Summary

• document that CodeCarbon directly focuses on CPU, GPU, and RAM power
• clarify that disk I/O, network transfers, displays, cooling, and peripherals are not separately modeled
• note that data movement or distributed workloads may need extra consideration

Fixes #154

Tests

• git diff --check
• uv run --only-group doc task docs

[davidberenstein1957]

Thanks for the contribution! I added some slight nuances :)

[davidberenstein1957]

Thanks for the contribution!

[benoit-cty]

Thanks for clarifying.