docs: record Frame mod feasibility and manager requirements

README.md

@@ -201,6 +201,7 @@ Frame's software fits together, all checked against a real headset and labelled
 | [Sideloading Linux and Windows games](docs/sideloading.md) | A .zip, folder or .exe as a Steam Devkit Game, runtime detection |
 | [Install links for websites](docs/web-install.md) | `frame-control://install` links and manifests, the rules, a button to paste |
 | [Steam games](docs/steam-games.md) · [VR video](docs/vr-video.md) · [WebXR in Chromium](docs/webxr-chromium.md) | Installing and buying, watching VR180/360, the Chromium build |
+| [VR mods and custom songs](docs/mods.md) | Per-game feasibility, real-Frame results and blockers; no installer yet |
 | [SSH](docs/ssh.md) · [Streaming](docs/streaming.md) · [Files](docs/file-transfer.md) · [Panels](docs/panels.md) · [Tailscale](docs/tailscale.md) | Topic notes |
 | [Frame Control for iPhone](docs/iphone.md) | The iPhone and iPad app, how it runs the server on the Frame, pairing |
 | [Recovery and OS images](docs/recovery-and-images.md) | Where to download the Frame's OS, what's inside, testing without the headset |