Add Privacy Policy document

Provide transparency about the extension's data handling and
permissions. Clarify that no personal data is collected or
transmitted, and all processing happens locally in the user's
browser.

- Explains cache status extension's privacy stance
- Outlines permissions used and their purposes
- Provides clear, accessible documentation

Author: bartTC

PRIVACY.md

@@ -0,0 +1,31 @@
+# Privacy Policy
+
+**Cache Status** does not collect, store, or transmit any personal data.
+
+## What the extension does
+
+- Reads HTTP response headers from pages you visit to detect cache status
+- Reads performance timing data from the browser's Navigation Timing API
+- Displays this information locally in the toolbar badge and popup
+
+## What the extension does NOT do
+
+- No data is sent to any server
+- No analytics or tracking
+- No cookies or local storage persistence
+- No third-party services
+
+All processing happens locally in your browser. When you close a tab, that tab's data is discarded.
+
+## Permissions explained
+
+| Permission | Why it's needed |
+|------------|-----------------|
+| `webRequest` | Read HTTP response headers |
+| `webNavigation` | Detect page loads |
+| `activeTab` | Access current tab info |
+| `<all_urls>` | Work on any website |
+
+## Contact
+
+Questions? Open an issue on [GitHub](https://github.com/bartTC/CacheStatusSafariExtension).