resubmit the lvgl code

APP_Framework/lib/lvgl/docs/porting/task-handler.md

@@ -0,0 +1,23 @@
+```eval_rst
+.. include:: /header.rst 
+:github_url: |github_link_base|/porting/task-handler.md
+```
+# Task Handler
+
+To handle the tasks of LVGL you need to call `lv_timer_handler()` periodically in one of the following:
+- *while(1)* of *main()* function 
+- timer interrupt periodically (lower priority than `lv_tick_inc()`)
+- an OS task periodically
+
+The timing is not critical but it should be about 5 milliseconds to keep the system responsive.
+
+Example:
+```c
+while(1) {
+  lv_timer_handler();
+  my_delay_ms(5);
+}
+```
+
+To learn more about timers visit the [Timer](/overview/timer) section.
+