Better supabase error message (#336)

Fixes #287

src/supabase_admin/supabase_context.ts

@@ -13,7 +13,9 @@ async function getPublishableKey({ projectId }: { projectId: string }) {
   );
 
   if (!publishableKey) {
-    throw new Error("No publishable key found for project");
+    throw new Error(
+      "No publishable key found for project. Make sure you are connected to the correct Supabase account and project. See https://dyad.sh/docs/integrations/supabase#no-publishable-keys",
+    );
   }
   return publishableKey.api_key;
 }