docs: add Linux DNS troubleshooting

[Anshumancanrock]

Description

Added a Linux-specific troubleshooting section to README for Docker DNS resolution failures during docker compose builds.

The new section includes:

• Symptoms (EAI_AGAIN, temporary name resolution failures)
• Docker daemon DNS configuration in /etc/docker/daemon.json
• Docker restart step
• Verification command inside a container
• Notes for systemd-resolved (127.0.0.53) and restricted network environments

Related Issue

Closes #396

Context

Some Linux setups (especially with systemd-resolved or rolling-release distributions) can fail DNS resolution during image builds. This blocks local onboarding and forces users into ad-hoc workarounds. Adding clear troubleshooting steps in README provides a standard and portable fix path.

How Has This Been Tested?

• Verified the README section placement and markdown formatting.
• Verified the documented commands are syntactically correct and actionable on Linux Docker setups.
• Confirmed scope is documentation-only (no runtime or source code changes).

Screenshots (if appropriate):

N/A

Types of changes

• Non-functional change (docs, style, minor refactor)
• 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 change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• All new and existing tests passed.

[cameri]

Thank you!!!