fix: Add C++ compiler prerequisite in readme

[srinivasrk]

Description

Adds a Windows-only prerequisite note to the setup documentation in README.md under Get Started → Prerequisites.
This documents the missing compiler fix: install Visual Studio Build Tools (if Visual Studio is not installed) and select the Desktop development with C++ workload.

Related Issues

• Closes #...
• Related to #...

Module(s) Affected

• docs (Documentation)
• agents
• api
• config
• core
• knowledge
• logging
• services
• tools
• utils
• web (Frontend)
• scripts
• tests
• Other: ...

Checklist

• I have read and followed the contribution guidelines.
• My code follows the project's coding standards.
• I have run pre-commit run --all-files and fixed any issues.
• I have added relevant tests for my changes.
• I have updated the documentation (if necessary).
• My changes do not introduce any new security vulnerabilities.

Additional Notes

This is a docs-only change intended to prevent Windows setup failures caused by missing C++ build tooling during dependency installation.

[srinivasrk]

This is needed for numpy build on windows.