Microsoft Bot framework: Sending Message on connect

Hook into the conversationUpdate event and check when the bot is added. After that, you can just post a message or begin a new dialog (as in the code below I extracted from the ContosoFlowers Node.js sample, though there are many others doing the same).

// Send welcome when conversation with bot is started, by initiating the root dialog
bot.on('conversationUpdate', function (message) {
    if (message.membersAdded) {
        message.membersAdded.forEach(function (identity) {
            if (identity.id === message.address.bot.id) {
                bot.beginDialog(message.address, "https://stackoverflow.com/");
            }
        });
    }
});