Updated Threads (markdown)

Threads.md

@@ -28,6 +28,8 @@ Note that this port does not use the GIL, otherwise the two cores would run in l
 
 We provide additional firmware variants for the Pyboard that enables the `_thread` module. It allows multiple concurrent threads sharing the single core with pre-emptive context switching.
 
+### Unix
+
 ### Resources
 
 * [Threads in MicroPython](https://www.youtube.com/watch?v=aDXgX0rGVDY): Damien's talk that introduced the feature