Merge pull request 'media URLs and nostr refs' (#71) from refs into main

Reviewed-on: Kieran/stream#71
Reviewed-by: Kieran <kieran@noreply.localhost>

src/hooks/placeholders.ts

@@ -0,0 +1,9 @@
+import { useMemo } from "react";
+
+export default function usePlaceholder(pubkey: string) {
+  const url = useMemo(
+    () => `https://robohash.v0l.io/${pubkey}.png?set=2`,
+    [pubkey]
+  );
+  return url;
+}