docs: add targets for the bundling debug (angular#60693)

PR Close angular#60693

Author: JeanMeche

packages/core/test/bundling/README.md

@@ -9,3 +9,18 @@ When doing renaming it is often necessary to update the gold files; to do so use
 yarn run symbol-extractor:check
 yarn run symbol-extractor:update
 ```
+
+## Debugging 
+
+You can inspect the build output of each project by using the `bundle.debug` target. 
+
+```
+yarn bazel build  //packages/core/test/bundling/standalone_bootstrap:bundle.debug
+```
+
+This target mostly tree shakes while keeping the symbols. To have a look at the minimal output (with inlining etc.) use the 
+`bundle.debug.min` target.
+
+```
+yarn bazel build  //packages/core/test/bundling/standalone_bootstrap:bundle.debug.min
+```