Add NOT_READY

Author: jedisct1

ChangeLog

@@ -14,6 +14,8 @@ servers is also supported with the new `-resolve name,address` syntax.
 is used, either for the list of servers or relays, the proxy ensures that
 relays and servers are on distinct networks.
  - Lying resolvers are detected and reported.
+ - New return code: `NOT_READY` for queries received before the proxy has
+been initialized.
  - Server lists can't be older than a week any more, even if directory
 permissions are incorrect and cache files cannot be written.
  - macOS/arm64 is now officially supported.