docs: add drone state vector guidance to getting_started.md

[DsThakurRawat]

Description

Added a callout in docs/getting_started.md instructing drone operators on formatting their state vectors (e.g., [roll, pitch, yaw, altitude]) instead of sending arm joint positions.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Infrastructure / CI update

How Has This Been Tested?

• pytest tests/ passes locally
• reflex doctor sanity check
• Other (please specify): Documentation verification only

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have kept the PR scoped to a single concern (one concern per PR)