chore(docs): add note about passkeys and 1password compat

Author: ndom91

docs/pages/getting-started/providers/passkey.mdx

@@ -212,3 +212,21 @@ export default function Login() {
 ## Options
 
 You can find all of the Passkeys provider options under the [API reference](/reference/core/providers/webauthn#webauthnconfig).
+
+## Notes
+
+- If you only pass a field named `username`, like below. 1Password **will not** offer to save new Passkeys in your login form.
+
+```ts filename="@/auth.ts" /username/
+providers = [
+  Passkey({
+    formFields: {
+      username: {
+        label: "Username",
+        required: true,
+        autocomplete: "webauthn username",
+      },
+    },
+  }),
+]
+```