message: Update README for event-listener
diff: @@ -6,8 +6,15 @@ This repository/package is not designed for productive usage. Instead it should
  ## How to use
  -Add a `EVENT_LISTENER_PRIV_KEY` variable that contains the private key to the root `.env` file.
  -Event listener will use this private key to perform transactions on-chain.
  +Edit your root .env file to the following properties:
  +
  +**REQUIRED**
  +- `EVENT_LISTENER_PRIV_KEY` variable that contains the private key to the root `.env` file. Event listener will use this private key to perform transactions on-chain.
  +
  +**OPTIONAL** (necessary for e-mail notifications)
  +- `MANDRILL_API_KEY` - API key generated in Mandrill (mandrill.com)
  +- `EMAIL_FROM` - E-mail from which you want to send email addresses
  +- `EMAIL_REPLY_TO` - E-mail to which we the users would be able to reply
  ### Run
  