docs: add DeepWiki badge to README (#50)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: roottool

README.md

@@ -2,6 +2,7 @@
 
 **The strict trust boundary for FormData.**
 
+[![Ask DeepWiki](https://deepwiki.com/badge.svg)](https://deepwiki.com/roottool/safe-formdata)
 [![npm version](https://img.shields.io/npm/v/safe-formdata)](https://www.npmjs.com/package/safe-formdata)
 [![CI](https://github.com/roottool/safe-formdata/actions/workflows/ci.yml/badge.svg)](https://github.com/roottool/safe-formdata/actions/workflows/ci.yml)
 [![codecov](https://codecov.io/gh/roottool/safe-formdata/graph/badge.svg)](https://codecov.io/gh/roottool/safe-formdata)