Closes #16

README.md

@@ -336,7 +336,8 @@ This matters because the same numeric identifier must not be confused between st
 
 Immutable runtime snapshot with a private frame index. Build it with
 `DbcDecodeBuilder::Build(parsed)` or construct it from `std::vector<DecodeFrame>`.
-Construction validates all definitions before publishing the snapshot and throws
+Construction validates all definitions and duplicate keys before building the lookup
+index or publishing the snapshot, and throws
 `std::invalid_argument` for invalid metadata, including manually supplied data:
 
 - Normalized CAN IDs must fit 11 bits for standard frames or 29 bits for extended