Merge pull request #2373 from iriark01/patch-3

Very minimal text

Author: sg-

DOXYGEN_FRONTPAGE.md

@@ -1,5 +1,8 @@
 # mbed OS code base
 
-This repo covers the mbed OS code base.
+This is the code documentation for mbed OS.
 
-For instructions on using the API, please see [insert link].
+For more information, please see:
+
+* [The mbed OS API References](https://docs.mbed.com/docs/mbed-os-api-reference/)
+* [The mbed OS Handbook](https://docs.mbed.com/docs/mbed-os-handbook/)