Merge pull request #17756 from gschorcht/doc/fix_getitng_started_docker

doc: small fix of "Getting Started" document structure in section docker

doc/doxygen/src/getting-started.md

@@ -308,6 +308,8 @@ The user on your computer requires permission to access and use docker. There ar
 - Your OS distribution may create a group called `docker`. If so, then adding yourself to that group (and logging out and in again) should grant you permission.
 - Execute docker with sudo. This is in fact the most secure and recommended setup (see [here](https://docs.docker.com/install/linux/linux-postinstall/), [here](https://docs.docker.com/engine/security/security/#docker-daemon-attack-surface), [here](https://www.projectatomic.io/blog/2015/08/why-we-dont-let-non-root-users-run-docker-in-centos-fedora-or-rhel/) and [here](https://fosterelli.co/privilege-escalation-via-docker.html)). No extra setup steps are needed. `make` should be instructed to use `sudo` by setting `DOCKER="sudo docker"` in the command line.
 
+### Downloading and testing RIOT docker container
+
 Finally, download the pre-built RIOT Docker container:
 
 ```console
@@ -321,7 +323,8 @@ This will take a while. If it finishes correctly, you can then use the toolchain
 $ docker run --rm -i -t -u $UID -v $(pwd):/data/riotbuild riot/riotbuild ./dist/tools/compile_test/compile_test.py
 ```
 
-# Usage
+Usage
+-----
 
 The RIOT build system provides support for using the Docker container to build RIOT projects, so you do not need to type the long docker command line every time:
 
@@ -350,8 +353,8 @@ Troubleshooting                                    {#docker-troubleshooting}
 
 On some Ubuntu versions a make with `BUILD_IN_DOCKER=1` can't resolve the host name of for example github.com. To fix this add the file `/etc/docker/daemon.json` with the address of your DNS Server.
 
-Generating `compile_commands.json` e.g. for code completion in IDEs
-===================================================================
+Generating compile_commands.json e.g. for code completion in IDEs
+=================================================================
 
 A `compile_commands.json` for the selected board can be generated by running inside the application
 folder the following: