message: docs: update Readme file with v 6.0 (Angular 11)
diff: @@ -15,6 +15,7 @@ See [Demo](https://ng-select.github.io/ng-select) page.
  | Angular| ng-select|
  | ------|:------:|
  +| >=11.0.0 <12.0.0 | v6.x |
  | >=10.0.0 <11.0.0 | v5.x |
  | >=9.0.0 <10.0.0 | v4.x |
  | >=8.0.0 <9.0.0 | v3.x |
  