add the md files from the docs repo to start updating them to v8

docs/porting/tick.md

@@ -0,0 +1,35 @@
+```eval_rst
+.. include:: /header.rst 
+:github_url: |github_link_base|/porting/tick.md
+```
+# Tick interface
+
+The LVGL needs a system tick to know the elapsed time for animation and other tasks.
+
+You need to call the `lv_tick_inc(tick_period)` function periodically and tell the call period in milliseconds. For example, `lv_tick_inc(1)` for calling in every millisecond.
+
+`lv_tick_inc` should be called in a higher priority routine than `lv_task_handler()` (e.g. in an interrupt) to precisely know the elapsed milliseconds even if the execution of `lv_task_handler` takes longer time.
+
+With FreeRTOS `lv_tick_inc` can be called in `vApplicationTickHook`.
+
+On Linux based operating system (e.g. on Raspberry Pi) `lv_tick_inc` can be called in a thread as below:
+```c
+void * tick_thread (void *args)
+{
+      while(1) {
+        usleep(5*1000);   /*Sleep for 5 millisecond*/
+        lv_tick_inc(5);      /*Tell LVGL that 5 milliseconds were elapsed*/
+    }
+}
+```
+
+
+
+## API
+
+```eval_rst
+
+.. doxygenfile:: lv_hal_tick.h
+  :project: lvgl
+
+```