docs: add info on setting up VSCode remote development using docker containers (#33790)

In f78bda9ff, recommended configuration files were added to be used as
basis for setting up [Remote Development using docker containers][1] in
VSCode. Apparently, I had forgotten to commit the corresponding
`README.md` file.

This commit adds `.devcontainer/README.md` with more info on Remote
Development in VSCode.

[1]: https://code.visualstudio.com/docs/remote/containers

PR Close #33790

.devcontainer/README.md

@@ -0,0 +1,31 @@
+# VSCode Remote Development - Developing inside a Containers
+
+This folder contains configuration files that can be used to opt into working on this repository in a [Docker container](https://www.docker.com/resources/what-container) via [VSCode](https://code.visualstudio.com/)'s Remote Development feature (see below).
+
+Info on remote development and developing inside a container with VSCode:
+- [VSCode: Remote Development](https://code.visualstudio.com/docs/remote/remote-overview)
+- [VSCode: Developing inside a Container](https://code.visualstudio.com/docs/remote/containers)
+- [VSCode: Remote Development FAQ](https://code.visualstudio.com/docs/remote/faq)
+
+
+## Usage
+
+_Prerequisite: [Install Docker](https://docs.docker.com/install) on your local environment._
+
+To get started, read and follow the instuctions in [Developing inside a Container](https://code.visualstudio.com/docs/remote/containers). The [.devcontainer/](.) directory contains pre-configured `devcontainer.json` and `Dockerfile` files, which you can use to set up remote development with a docker container.
+
+In a nutshell, you need to:
+- Install the [Remote - Containers](https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.remote-containers) extension.
+- Copy [recommended-Dockerfile](./recommended-Dockerfile) to `Dockerfile` (and optionally tweak to suit your needs).
+- Copy [recommended-devcontainer.json](./recommended-devcontainer.json) to `devcontainer.json` (and optionally tweak to suit your needs).
+- Open VSCode and bring up the [Command Palette](https://code.visualstudio.com/docs/getstarted/userinterface#_command-palette).
+- Type `Remote-Containers: Open Folder in Container` and choose your local clone of [angular/angular](https://github.com/angular/angular).
+
+The `.devcontainer/devcontainer.json` and `.devcontainer/Dockerfile` files are ignored by git, so you can have your own local versions. We may occasionally update the template files ([recommended-devcontainer.json](./recommended-devcontainer.json), [recommended-Dockerfile](./recommended-Dockerfile)), in which case you will need to manually update your local copies (if desired).
+
+
+## Updating `recommended-devcontainer.json` and `recommended-Dockerfile`
+
+You can update and commit the recommended config files (which people use as basis for their local configs), if you find that something is broken, out-of-date or can be improved.
+
+Please, keep in mind that any changes you make will potentially be used by many people on different environments. Try to keep these config files cross-platform compatible and free of personal preferences.

.devcontainer/recommended-Dockerfile

@@ -1,5 +1,5 @@
 # Image metadata and config.
-FROM circleci/node:10-browsers
+FROM circleci/node:10-browsers  # This needs to be in sync with what we use on CI.
 
 LABEL name="Angular dev environment" \
       description="This image can be used to create a dev environment for building Angular." \
@@ -15,7 +15,7 @@ USER root
 
 # Configure `Node.js`/`npm` and install utilities.
 RUN npm config --global set user root
-RUN npm install --global yarn@1.13.0  # This needs to be in sync with what we use on CI.
+RUN npm install --global yarn@1.19.1  # This needs to be in sync with what we use on CI.
 
 
 # Go! (And keep going.)

.gitignore

@@ -13,6 +13,7 @@ pubspec.lock
 .c9
 .idea/
 .devcontainer/*
+!.devcontainer/README.md
 !.devcontainer/recommended-devcontainer.json
 !.devcontainer/recommended-Dockerfile
 .settings/