Fix docs.rs build of dioxus-lib (#4321)

packages/dioxus-lib/src/lib.rs

@@ -1,4 +1,5 @@
 #![doc = include_str!("../README.md")]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 #![doc(html_logo_url = "https://avatars.githubusercontent.com/u/79236386")]
 #![doc(html_favicon_url = "https://avatars.githubusercontent.com/u/79236386")]