docs(readme): use markdown images so Gogs rewrites relative paths (HTML <img> wasn't resolving)

Session-Id: 481d7b9c

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -6,14 +6,15 @@ A fork of [vercel-labs/json-render](https://github.com/vercel-labs/json-render)
 
 ![json-render playground: one sentence becomes a working UI](docs/demo.jpg)
 
-<sub>One sentence → a full landing page. JSON spec on the left, live preview (real-photo gallery + pricing cards) on the right.</sub>
-
-<table>
-<tr>
-<td width="50%"><img src="docs/demo-lightbox.jpg" alt="Lightbox component"/><br/><sub><b>Lightbox</b> — click a thumbnail → fullscreen, prev/next, Esc to close</sub></td>
-<td width="50%"><img src="docs/demo-modal.jpg" alt="Modal component"/><br/><sub><b>Modal</b> — click a button → centered popup form, Esc / backdrop / ✕ to close</sub></td>
-</tr>
-</table>
+*One sentence → a full landing page: JSON spec on the left, live preview (real-photo gallery + pricing cards) on the right.*
+
+**Lightbox** — click a thumbnail for a fullscreen gallery (prev/next, Esc to close):
+
+![Lightbox component](docs/demo-lightbox.jpg)
+
+**Modal** — click a button for a centered popup form (Esc / backdrop / ✕ to close):
+
+![Modal component](docs/demo-modal.jpg)
 
 ## What this fork adds