docs: Update README for Angular 15 support

  - Add Angular 15 installation instructions as latest version
  - Update version compatibility table
  - Move Angular 14 to specific version installation

Author: t-ho

README.md

@@ -43,7 +43,8 @@ $ yarn add ngx-ui-loader
 
 | Angular       | Installation                        | Documentation                                                         |
 | ------------- | ----------------------------------- | --------------------------------------------------------------------- |
-| Angular 14    | `npm i --save ngx-ui-loader`        | [v14.x.x](https://tdev.app/ngx-ui-loader)                             |
+| Angular 15    | `npm i --save ngx-ui-loader`        | [v15.x.x](https://tdev.app/ngx-ui-loader)                             |
+| Angular 14    | `npm i --save [email protected]` | [v14.x.x](https://tdev.app/ngx-ui-loader)                             |
 | Angular 13    | `npm i --save [email protected]` | [v13.x.x](https://tdev.app/ngx-ui-loader)                             |
 | Angular 11    | `npm i --save [email protected]` | [v11.x.x](https://tdev.app/ngx-ui-loader)                             |
 | Angular 10    | `npm i --save [email protected]` | [v10.x.x](https://tdev.app/ngx-ui-loader)                             |