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

docs/porting/os.md

@@ -0,0 +1,21 @@
+```eval_rst
+.. include:: /header.rst 
+:github_url: |github_link_base|/porting/os.md
+```
+# Operating system and interrupts
+
+LVGL is **not thread-safe** by default.
+
+However, in the following conditions it's valid to call LVGL related functions:
+- In *events*. Learn more in [Events](/overview/event).
+- In *lv_tasks*. Learn more in [Tasks](/overview/task).
+
+
+## Tasks and threads
+If you need to use real tasks or threads, you need a mutex which should be invoked before the call of `lv_task_handler` and released after it.
+Also, you have to use the same mutex in other tasks and threads around every LVGL (`lv_...`) related function calls and codes.
+This way you can use LVGL in a real multitasking environment. Just make use of a mutex to avoid the concurrent calling of LVGL functions.
+
+## Interrupts
+Try to avoid calling LVGL functions from the interrupts (except `lv_tick_inc()` and `lv_disp_flush_ready()`). But, if you need to do this you have to disable the interrupt which uses LVGL functions while `lv_task_handler` is running.
+It's a better approach to set a flag or some value and periodically check it in an `lv_task`.