chore: vendor clipboard into go package

packages/tui/clipboard/cmd/gclip-gui/README.md

@@ -0,0 +1,31 @@
+# gclip-gui
+
+This is a very basic example for verification purpose that demonstrates
+how the [golang.design/x/clipboard](https://golang.design/x/clipboard)
+can interact with macOS/Linux/Windows/Android/iOS system clipboard.
+
+The gclip GUI application writes a string to the system clipboard
+periodically then reads it back and renders it if possible.
+
+Because of the system limitation, on mobile devices, only string data is
+supported at the moment. Hence, one must use clipboard.FmtText. Other supplied
+formats result in a panic.
+
+This example is intentded as cross platform application. To build it, one
+must use [gomobile](https://golang.org/x/mobile). You may follow the instructions
+provided in the [GoMobile wiki](https://github.com/golang/go/wiki/Mobile) page.
+
+
+- For desktop: `go build -o gclip-gui`
+- For Android: `gomobile build -v -target=android -o gclip-gui.apk`
+- For iOS:     `gomobile build -v -target=ios -bundleid design.golang.gclip-gui.app`
+
+## Screenshots
+
+| macOS | iOS | Windows | Android | Linux |
+|:-----:|:---:|:-------:|:-------:|:-----:|
+|![](../../tests/testdata/darwin.png)|![](../../tests/testdata/ios.png)|![](../../tests/testdata/windows.png)|![](../../tests/testdata/android.png)|![](../../tests/testdata/linux.png)|
+
+## License
+
+MIT | © 2021 The golang.design Initiative Authors, written by [Changkun Ou](https://changkun.de).