Added comments to README.md and badge.

diff --git a/README.md b/README.md
index c8946d18097474fbceff99a222ed8e2096a3b244..cd8c10a7c9c3295266916029400c109a2da6bd9a 100644 (file)
--- a/README.md
+++ b/README.md
@@ -57,12 +57,28 @@ https://www.dealii.org.
 Continuous Integration Status:
 ------------------------
 
-| System | Status | More information |
-| --- | --- | --- |
-| Indent | ![indent](https://github.com/dealii/dealii/workflows/indent/badge.svg) | using GitHub actions |
-| Linux | [![Build Status](https://jenkins.tjhei.info/job/dealii/job/master/badge/icon)](https://jenkins.tjhei.info/job/dealii/job/master/) | See https://jenkins.tjhei.info |
-| MacOS | [![Build Status](https://jenkins.tjhei.info/job/dealii-OSX/job/master/badge/icon)](https://jenkins.tjhei.info/job/dealii-OSX/job/master/) | See https://jenkins.tjhei.info |
-| MacOS | [![Build Status](https://github.com/dealii/dealii/workflows/github-CI/badge.svg)](https://github.com/dealii/dealii/actions?query=workflow%3Agithub-CI) | See https://github.com/dealii/dealii/actions |
-| MSVC | [![Build status](https://github.com/dealii/dealii/workflows/github-windows/badge.svg)](https://github.com/dealii/dealii/actions?query=workflow%3Agithub-windows) | See https://github.com/dealii/dealii/actions |
-| CDash | [![cdash](https://img.shields.io/website?down_color=lightgrey&down_message=offline&label=CDash&up_color=green&up_message=up&url=https%3A%2F%2Fcdash.43-1.org%2Findex.php%3Fproject%3Ddeal.II)](https://cdash.43-1.org/index.php?project=deal.II) | Various builds and configurations on https://cdash.43-1.org/index.php?project=deal.II |
+| System | Status                                                                                                                                                                                                                                           | More information                                                                      |
+| ------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------- |
+| Indent | ![indent](https://github.com/dealii/dealii/workflows/indent/badge.svg)                                                                                                                                                                           | using GitHub actions                                                                  |
+| Linux  | [![Build Status](https://jenkins.tjhei.info/job/dealii/job/master/badge/icon)](https://jenkins.tjhei.info/job/dealii/job/master/)                                                                                                                | See https://jenkins.tjhei.info                                                        |
+| MacOS  | [![Build Status](https://jenkins.tjhei.info/job/dealii-OSX/job/master/badge/icon)](https://jenkins.tjhei.info/job/dealii-OSX/job/master/)                                                                                                        | See https://jenkins.tjhei.info                                                        |
+| MacOS  | [![Build Status](https://github.com/dealii/dealii/workflows/github-CI/badge.svg)](https://github.com/dealii/dealii/actions?query=workflow%3Agithub-CI)                                                                                           | See https://github.com/dealii/dealii/actions                                          |
+| MSVC   | [![Build status](https://github.com/dealii/dealii/workflows/github-windows/badge.svg)](https://github.com/dealii/dealii/actions?query=workflow%3Agithub-windows)                                                                                 | See https://github.com/dealii/dealii/actions                                          |
+| Docker | [![Build status](https://github.com/dealii/dealii/workflows/github-docker/badge.svg)](https://github.com/dealii/dealii/actions?query=workflow%3Agithub-docker)                                                                                   | See https://github.com/dealii/dealii/actions                                          |
+| CDash  | [![cdash](https://img.shields.io/website?down_color=lightgrey&down_message=offline&label=CDash&up_color=green&up_message=up&url=https%3A%2F%2Fcdash.43-1.org%2Findex.php%3Fproject%3Ddeal.II)](https://cdash.43-1.org/index.php?project=deal.II) | Various builds and configurations on https://cdash.43-1.org/index.php?project=deal.II |
+
+Docker Images:
+-------------
+
+Docker images based on the Ubuntu operating system are available on
+[Docker Hub](https://hub.docker.com/repository/docker/dealii/dealii). You can 
+use any of the available version 
+([list of available tags](https://hub.docker.com/repository/docker/dealii/dealii/tags)) 
+by running, for example:
+
+    $ docker run --rm -t -i dealii/dealii:master-focal
+
+The above command would drop you into an isolated environment, in which you 
+will find the latest version of deal.II (master development branch) installed
+under `/usr/local`.