message: explanation of read-modes added to nodeos --help
diff: @@ -184,7 +184,10 @@ void chain_plugin::set_program_options(options_description& cli, options_descrip
  ("key-blacklist", boost::program_options::value<vector<string>>()->composing()->multitoken(),
  "Public key added to blacklist of keys that should not be included in authorities (may specify multiple times)")
  ("read-mode", boost::program_options::value<eosio::chain::db_read_mode>()->default_value(eosio::chain::db_read_mode::SPECULATIVE),
  - "Database read mode (\"speculative\" or \"head\")")
  + "Database read mode (\"speculative\", \"head\" or \"irreversible\").\n"
  + "In \"speculative\" mode database contains changes done up to the head block plus changes made by transactions not yet included to the blockchain.\n"
  + "In \"head\" mode database contains changes done up to the current head block.\n"
  + "In \"irreversible\" mode database contains changes done up the current irreversible block.\n")
  ;
  // TODO: rate limiting
  