Update docs

docs/README.md

@@ -1111,9 +1111,8 @@ int mg_tls_init(struct mg_connection *c, struct mg_tls_opts *opts);
 Initialise TLS on a given connection.
 
 IMPORTANT: mbedTLS implementation uses `mg_random` as RNG. The `mg_random`
-is defined as weak, therefore it is possible to override Mongoose's `mg_random`
-with a custom implementation. Just create your own `mg_random` function:
-`void mg_random(void *buf, size_t len)`.
+can be overridden by setting `MG_ENABLE_CUSTOM_RANDOM` and defining
+your own `mg_random()` implementation.
 
 
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