Mention BIP155 in doc/bips.md
Mention BIP155 in doc/bips.md


Former-commit-id: d2480ea319517a699ec0b67f3bf8020c33d181df
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin