Detailed description

Improve the Usage section in the README with a better description on how to use this plugin. Maybe I'm dumb, but I spent several minutes looking for the small Redoc tab at the bottom left of my OpenAPI file. A short description of the added tab and/or a screenshot would be appreciated.

Context

Ease the plugin adoption from new users.

Your environment

• Version used: Jetbrains JRE, IntelliJ IDEA 2019.3
• Operating system and version: Archlinux