Document tunnels' optional options better

[nonlin-lin-chaos-order-etc-etal]

https://github.com/PurpleI2P/i2pd/blob/c010c83654e5c7baabf492f82aa43999eacaf44a/ClientContext.cpp#L400 :

client:

# optional parameters (may be omitted)
    std::string keys = section.second.get (I2P_CLIENT_TUNNEL_KEYS, "");
    std::string address = section.second.get (I2P_CLIENT_TUNNEL_ADDRESS, "127.0.0.1");
    int destinationPort = section.second.get (I2P_CLIENT_TUNNEL_DESTINATION_PORT, 0);
    i2p::data::SigningKeyType sigType = section.second.get (I2P_CLIENT_TUNNEL_SIGNATURE_TYPE, i2p::data::SIGNING_KEY_TYPE_ECDSA_SHA256_P256);

server:

# optional parameters (may be omitted)
    int inPort = section.second.get (I2P_SERVER_TUNNEL_INPORT, 0);
    std::string accessList = section.second.get (I2P_SERVER_TUNNEL_ACCESS_LIST, "");
    std::string hostOverride = section.second.get (I2P_SERVER_TUNNEL_HOST_OVERRIDE, "");
    std::string webircpass = section.second.get<std::string> (I2P_SERVER_TUNNEL_WEBIRC_PASSWORD, "");
    bool gzip = section.second.get (I2P_SERVER_TUNNEL_GZIP, true);
    i2p::data::SigningKeyType sigType = section.second.get (I2P_SERVER_TUNNEL_SIGNATURE_TYPE, i2p::data::SIGNING_KEY_TYPE_ECDSA_SHA256_P256);
    uint32_t maxConns = section.second.get(i2p::stream::I2CP_PARAM_STREAMING_MAX_CONNS_PER_MIN, i2p::stream::DEFAULT_MAX_CONNS_PER_MIN);
    std::string address = section.second.get<std::string> (I2P_SERVER_TUNNEL_ADDRESS, "127.0.0.1");
    bool isUniqueLocal = section.second.get(I2P_SERVER_TUNNEL_ENABLE_UNIQUE_LOCAL, true);

[l-n-s]

Everything is documented, except maxConns