resolves elastic#88333

Fixed:

- add note that `secure: false` will use TLS, but after an initial connection
  with TCP; we have been getting questions from customers who believed that
  `secure: false` implied TLS was not used at all.

- added a link to the nodemailer "well-known services" module, to allow
  customers to see examples of other email service configurations

- updated the Outlook config example to use the current nodemailer values

- couple of other small tweaks