Added error for devices not having TRNG

README.md

@@ -1,6 +1,7 @@
 # TLSSocket example for Mbed OS
 
 This examples application demonstrates the usage of `TLSSocket` API. To understand how secure sockets work in Mbed OS, please refer to the [Documentation](#documentation) section below.
+**NOTE**: This example works only on devices having TRNG supported!
 
 ### Selecting the network interface
 

main.cpp

@@ -1,6 +1,10 @@
 #include "mbed.h"
 #include "mbed_trace.h"
 
+#ifndef DEVICE_TRNG
+#error "mbed-os-example-tls-socket requires a device which supports TRNG"
+#else
+
 const char cert[] = \
     "-----BEGIN CERTIFICATE-----\n"
     "MIIENjCCAx6gAwIBAgIBATANBgkqhkiG9w0BAQUFADBvMQswCQYDVQQGEwJTRTEU\n"
@@ -105,3 +109,4 @@ int main(void)
     net->disconnect();
     printf("Done\n");
 }
+#endif