docs: add dev-app section to contributing docs

docs: link directly to dev-app `README.md`

Author: michael-small

contributing-docs/building-and-testing-angular.md

@@ -6,6 +6,7 @@ It also explains the basic mechanics of using `git`, `node`, and `pnpm`.
 - [Building and Testing Angular](#building-and-testing-angular)
   - [Prerequisite Software](#prerequisite-software)
   - [Development in a Container](#development-in-a-container)
+  - [Experimenting in dev-app](#experimenting-in-dev-app)
   - [Getting the Sources](#getting-the-sources)
   - [Installing NPM Modules](#installing-npm-modules)
   - [Building](#building)
@@ -57,6 +58,10 @@ following on your development machine:
 
 You can also use the provided [Dev Container](https://containers.dev/) configuration to set up a development environment. This approach uses Docker to create a container with all the necessary tools (Node.js, pnpm, etc.) pre-installed.
 
+## Experimenting in dev-app
+
+For experimentation while developing Angular, consider running the [dev-app](../dev-app/README.md) in this repository.
+
 **Prerequisites:**
 
 - [Docker Desktop](https://www.docker.com/products/docker-desktop)