add warning about enabling public_instance setting

searx/__init__.py

@@ -104,3 +104,9 @@ if max_request_timeout is None:
     logger.info('max_request_timeout=%s', repr(max_request_timeout))
 else:
     logger.info('max_request_timeout=%i second(s)', max_request_timeout)
+
+if settings['server']['public_instance']:
+    logger.warning(
+        "Be aware you have activated features intended only for public instances. "
+        + "This force the usage of the bot limiter and link_token plugins."
+    )