docs: add comprehensive E2E Markdown test document and update README

- Added a new document `docs/e2e.md` that serves as an end-to-end test for various Markdown features.
- Updated `README.md` to include a link to the new E2E Markdown test document.

Author: cyanxiao

README.md

@@ -55,3 +55,4 @@ For detailed usage instructions, configuration options, and advanced features, s
 - [Usage Guide](docs/usage-guide.md) - Complete configuration examples and input/output reference
 - [Features](docs/features.md) - Detailed documentation for One Entry Mode, Page Replacement, and Internal Link Resolution
 - [Development](docs/development.md) - Setup, testing, and contribution guidelines
+- [E2E Markdown Test](docs/e2e.md) - Comprehensive Markdown syntax test document showcasing all supported features