docs: add safety note

src/main.rs

@@ -189,6 +189,18 @@ impl State {
         widget::image::allocate(widget::image::Handle::from_rgba(
             image.width(),
             image.height(),
+            // SAFETY: this is a sort of race condition;
+            // will cause panics with large enough images,
+            // when they are edited consecutively.
+            //
+            // this can be reproduced by holding down 'i' with a 10k by 10k px image,
+            // which will invert the colors rapidly and eventually crash the app.
+            //
+            // however, that is not such a problem in this case,
+            // and I don't know a different way of doing this that doesn't copy
+            // (performance loss, which is can be pretty big)
+            // or likely cause flickering instead in such cases
+            // (like using Handle over Allocation to immediately drop the last one)
             unsafe { std::mem::transmute::<&[u8], &'static [u8]>(image.as_bytes()) },
         ))
         .map(Message::ImageDisplayReady)