message: docs: describe when features can be unavailable
diff: @@ -46,6 +46,12 @@ But so far some things still need manual modification and that is done by files
  To maintain the package by myself without waiting for external reviews.
  +## Why is my fancy API still not available here?
  +
  +A feature needs to be supported by more than two major browser engines to be included here, to make sure there is a good consensus among vendors: __Gecko__ (Firefox), __Blink__ (Chrome/Edge), and __WebKit__ (Safari).
  +
  +If the condition is met but still is not available here, please [file an issue](https://github.com/saschanaz/types-web/issues/new).
  +
  ## Build Instructions
  * To get things setup:
  