Fully automate dev setup with Gitpod

This commit implements a fully-automated development setup using Gitpod.io, an
online IDE for GitHub and GitLab that enables Dev-Environments-As-Code.
This makes it easy for anyone to get a ready-to-code workspace for any branch,
issue or pull request almost instantly with a single click.

.gitpod.Dockerfile

@@ -0,0 +1,7 @@
+FROM gitpod/workspace-full
+
+# Install custom tools, runtimes, etc.
+# For example "bastet", a command-line tetris clone:
+# RUN brew install bastet
+#
+# More information: https://www.gitpod.io/docs/config-docker/

.gitpod.yml

@@ -0,0 +1,6 @@
+image:
+  file: .gitpod.Dockerfile
+
+tasks:
+  - init: 'echo "TODO: Replace with init/build command"'
+    command: 'echo "TODO: Replace with command to start project"'

README.md

@@ -1,3 +1,5 @@
+[![Gitpod ready-to-code](https://img.shields.io/badge/Gitpod-ready--to--code-blue?logo=gitpod)](https://gitpod.io/#https://github.com/corona-warn-app/cwa-documentation)
+
 <p align="center">
  <a href="https://www.coronawarn.app/en/"><img src="https://raw.githubusercontent.com/corona-warn-app/cwa-documentation/master/images/CWA_title.png" width="400"></a>
 </p>