chore(readme): add link to Deep Wiki for automated code documentation (#1735)

Deep Wiki from Cognition Labs already has some useful documentation that
they generated for us: https://deepwiki.com/unraid/api. This PR adds
their badge to our readme so contributors can access their documentation
directly.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- Documentation
- Added an “Ask DeepWiki” shield badge to the top of the README’s
project shields, giving users quick access to a dedicated Q&A/help
resource.
- Improves discoverability of support and learning materials directly
from the project homepage.
- No functional or behavioral changes to the application; this is an
informational enhancement aimed at easing onboarding and providing
faster guidance for users exploring the project.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: pujitm

readme.md

@@ -21,6 +21,8 @@
 [![LinkedIn][linkedin-shield]][linkedin-url]
 [![Codecov][codecov-shield]][codecov-url]
 
+[![Ask DeepWiki](https://deepwiki.com/badge.svg)](https://deepwiki.com/unraid/api)
+
 </div>
 <!-- PROJECT LOGO -->
 <br />