Rtos API example

Revision:
0:9fca2b23d0ba
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os/drivers/mbed_lib.json	Sat Feb 23 12:13:36 2019 +0000
@@ -0,0 +1,13 @@
+{
+    "name": "drivers",
+    "config": {
+        "uart-serial-txbuf-size": {
+            "help": "Default TX buffer size for a UARTSerial instance (unit Bytes))",
+            "value": 256
+        },
+        "uart-serial-rxbuf-size": {
+            "help": "Default RX buffer size for a UARTSerial instance (unit Bytes))",
+            "value": 256
+        }
+    }
+}