docs: mention lack of Wayland support (#81)

Author: changkun

README.md

@@ -128,7 +128,9 @@ accessing system clipboards, but here are a few details you might need to know.
 ### Dependency
 
 - macOS: require Cgo, no dependency
-- Linux: require X11 dev package. For instance, install `libx11-dev` or `xorg-dev` or `libX11-devel` to access X window system.
+ - Linux: require X11 dev package. For instance, install `libx11-dev` or `xorg-dev` or `libX11-devel` to access X window system.
+   Wayland sessions are currently unsupported; running under Wayland
+   typically requires an XWayland bridge and `DISPLAY` to be set.
 - Windows: no Cgo, no dependency
 - iOS/Android: collaborate with [`gomobile`](https://golang.org/x/mobile)