Add missing warning in doc
Found by Nicholas Wilson
fixes #288
diff --git a/include/polarssl/config.h b/include/polarssl/config.h
index 3a18f8a..b7d8b6b 100644
--- a/include/polarssl/config.h
+++ b/include/polarssl/config.h
@@ -331,8 +331,9 @@
* If set, the X509 parser will not break-off when parsing an X509 certificate
* and encountering an unknown critical extension.
*
- * Uncomment to prevent an error.
+ * \warning Depending on your PKI use, enabling this can be a security risk!
*
+ * Uncomment to prevent an error.
#define POLARSSL_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION
*/