Rtos API example

Revision:
0:9fca2b23d0ba
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Sat Feb 23 12:13:36 2019 +0000
@@ -0,0 +1,1 @@
+https://github.com/ARMmbed/mbed-os.git/#4e222952d757e378d5a591ca7fd143dcda24fc7e