Mention sample program execution with Linux framebuffer in README.md

Author: shengwen-tw

README.md

@@ -72,13 +72,20 @@ Build the library and demo program.
 $ make
 ```
 
-Run sample `Mado` program:
+`Mado` supports SDL or Linux framebuffer as backends.
+
+Run sample `Mado` program with SDL backend:
 ```shell
 $ ./demo-sdl
 ```
 
 Once the window appears, you should be able to move the windows and interact with the widgets.
 
+Run sample `Mado` program with Linux framebuffer backend:
+```shell
+$ sudo FRAMEBUFFER=/dev/fb0 ./demo-fbdev
+```
+
 ## License
 
 `Mado` is available under a MIT-style license, permitting liberal commercial use.