docs: mark @angular-devkit/build-optimizer as deprecated.

dgp1130 · filipesilva · commit 5e435ff37703 · 2021-10-06T14:34:59.000-05:00
DEPRECATED: `@angular-devkit/build-optimizer`

It's functionality has been included in `@angular-devkit/build-angular` so this package is no longer needed by the CLI and we will stop publishing the package soon. It has been an experimental (never hit `1.0.0`) and internal (only used by Angular itself) package and should be not be used directly by others.
diff --git a/packages/angular_devkit/build_optimizer/README.md b/packages/angular_devkit/build_optimizer/README.md
@@ -2,6 +2,11 @@
 
 Angular Build Optimizer contains Angular optimizations applicable to JavaScript code as a TypeScript transform pipeline.
 
+This package is **deprecated** and should not be used. It has always been experimental (never hit
+`1.0.0`) and was an internal package for the Angular CLI. All the relevant functionality has been
+moved into
+[`@angular-devkit/build-angular`](https://npmjs.com/package/@angular-devkit/build-angular).
+
 ## Available optimizations
 
 Transformations applied depend on file content:
