doc: libbitcoinconsensus: add missing error code description, fix NBitcoin link

doc/shared-libraries.md

@@ -41,9 +41,10 @@ The interface is defined in the C header `bitcoinconsensus.h` located in `src/sc
 - `bitcoinconsensus_ERR_TX_SIZE_MISMATCH` - `txToLen` did not match with the size of `txTo`
 - `bitcoinconsensus_ERR_DESERIALIZE` - An error deserializing `txTo`
 - `bitcoinconsensus_ERR_AMOUNT_REQUIRED` - Input amount is required if WITNESS is used
+- `bitcoinconsensus_ERR_INVALID_FLAGS` - Script verification `flags` are invalid (i.e. not part of the libconsensus interface)
 
 ### Example Implementations
-- [NBitcoin](https://github.com/NicolasDorier/NBitcoin/blob/master/NBitcoin/Script.cs#L814) (.NET Bindings)
+- [NBitcoin](https://github.com/MetacoSA/NBitcoin/blob/5e1055cd7c4186dee4227c344af8892aea54faec/NBitcoin/Script.cs#L979-#L1031) (.NET Bindings)
 - [node-libbitcoinconsensus](https://github.com/bitpay/node-libbitcoinconsensus) (Node.js Bindings)
 - [java-libbitcoinconsensus](https://github.com/dexX7/java-libbitcoinconsensus) (Java Bindings)
 - [bitcoinconsensus-php](https://github.com/Bit-Wasp/bitcoinconsensus-php) (PHP Bindings)