docs: add shared build requisites guide

[adriangibanelbtactic]

Summary

This PR adds a shared build prerequisites document and links it from both build and development entry points.

Problem

Build prerequisites (Docker user setup and SSH key preparation) were not centralized, so setup guidance could diverge between build/README.md and develop/README.md.

Approach

• Added a new shared document: build/BUILD_REQUISITES.md
• Linked the page from:
  • build/README.md
  • develop/README.md

Scope

Documentation-only change. No runtime, build scripts, or source code behavior changed.

Issue Link

• Closes Build Documentation. Docker and Github user keys explanation should be added. #88
• Closes Build Documentation. Docker driver setup is implied #89

Testing

• Verified markdown structure and links are correct in changed files.
• No code tests required for this docs-only change.

[adriangibanelbtactic]

Do you think it's actually worth adding a 'Readme for agents only' section in the same document that instruct an agent how to run docker command to know if it's actually using Docker-CE or podman's docker wrapper ?