Mbed TLS details for Mbed OS

Information on how Mbed TLS is shipped with Mbed OS and details on what's included.

Author: Marcelo Salazar

docs/reference/api/security/TLS.md

@@ -2,6 +2,8 @@
 
 Arm Mbed TLS provides a comprehensive SSL/TLS solution and makes it easy for developers to include cryptographic and SSL/TLS capabilities in their software and embedded products. As an SSL library, it provides an intuitive API, readable source code and a minimal and highly configurable code footprint.
 
+Mbed TLS has been adapted and pre-integrated with Mbed OS [here](https://github.com/ARMmbed/mbed-os/tree/master/features/mbedtls). It's imported from its standalone [release](https://github.com/ARMmbed/mbedtls). This edition of mbed TLS does not include test code or the scripts used in the development of the library. All of these can be found in the standalone release.
+
 <span class="notes">**Note:** Mbed TLS needs a secure source of random numbers; make sure that your target board has one and that it is fully ported to Arm Mbed OS. You can read more about this in our [porting guide](/docs/development/reference/contributing.html).</span>
 
 ### Mbed TLS examples