I prepared a presentation about HTTPS for my collegues about a month ago. It contained some information of why we should switch to HTTPS right away, how to get free certificates from let's encrypt and what should you consider when doing such migration. Also I made an overview of various https-related terms and partially told about http/2.
Presentation slides can be found here.
Also you can find presentation sources on my github. By the way, presentation itself is made in React with the help of spectacle library.