docs: added documentation

src/lib.rs

@@ -454,6 +454,13 @@ impl<T: futures_io::AsyncSeek> tokio::io::AsyncSeek for Compat<T> {
     }
 }
 
+/// Manually enter the tokio runtime.
+///
+/// This function returns the [`EnterGuard`] which keeps the tokio runtime active until it is
+/// dropped. Use this function when you cannot use one of the preexisting wrappers this crate
+/// provides.
+///
+/// TODO: Examples
 pub fn enter_tokio_runtime() -> EnterGuard<'static> {
     TOKIO1.handle.enter()
 }