doc: Add missing indexes/blockfilter/basic/ to doc/files.md
doc: Add missing indexes/blockfilter/basic/ to doc/files.md

Former-commit-id: 3249383d506fe5b4063179eb9b0678dd65a5e328
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin