README: Add section to FAQ about how to work with async code

README.md

@@ -309,6 +309,14 @@ Here is an example (from https://github.com/AlexxxRu/TinyPomodoro):
 
 <img src="media/pompodoro-skin.png" width="50%">
 
+### How do I use egui with `async`?
+If you call `.await` in your GUI code, the UI will freeze, with is very bad UX. Instead, keep the GUI thread non-blocking and communicate with any concurrent tasks (`async` tasks or other threads) with something like:
+* Channels (e.g. [`std::sync::mpsc::channel`](https://doc.rust-lang.org/std/sync/mpsc/fn.channel.html)). Make sure to use [`try_recv`](https://doc.rust-lang.org/std/sync/mpsc/struct.Receiver.html#method.try_recv) so you don't block the gui thread!
+* `Arc<Mutex<Value>>` (background thread sets a value; GUI thread reads it)
+* [`poll_promise::Promise`](https://docs.rs/poll-promise) (example: [`eframe/examples/download_image.rs`](https://github.com/emilk/egui/blob/master/eframe/examples/download_image.rs))
+* [`eventuals::Eventual`](https://docs.rs/eventuals/latest/eventuals/struct.Eventual.html)
+* [`tokio::sync::watch::channel`](https://docs.rs/tokio/latest/tokio/sync/watch/fn.channel.html)
+
 ### What about accessibility, such as screen readers?
 There is experimental support for a screen reader. In [the web demo](https://www.egui.rs/#demo) you can enable it in the "Backend" tab.