docs: add instructions to preview webapp locally

Author: alejoe91

README.md

@@ -12,4 +12,15 @@ See:
 The format of probes is JSON-based. See [documentation](https://probeinterface.readthedocs.io/en/main/format_spec.html) for full specifications.
 
 
-  
+### Preview `probe-viewer` app locally
+
+To build and preview the `probe-viewer` web-app locally:
+
+```bash
+cd apps/probe-viewer
+uv run build.py
+# build
+npm run build
+# run
+npx vite preview
+```