docs: added missing sub-header

README.md

@@ -42,6 +42,8 @@ For the optimal setup, ensure you have:
 ./gradlew build
 ```
 
+### Docker build
+
 The default docker base image is `azul/zulu-openjdk-alpine:21-jre`. This is customizable via the docker build arg `DOCKER_BASE_IMAGE`.
 Please note that the default helm values configure the kafka compression type `snappy` which requires gcompat to be installed in the resulting image.
 So either provide a base image with gcompat installed or change/disable the compression type in the helm values.
@@ -120,4 +122,4 @@ A brief summary follows below:
 
 The [reuse tool](https://github.com/fsfe/reuse-tool) can be used to verify and establish compliance when new files are added.
 
-For more information on the reuse tool visit https://github.com/fsfe/reuse-tool.
+For more information on the reuse tool visit https://github.com/fsfe/reuse-tool.