README: use consistent heading style

README.md

@@ -55,7 +55,7 @@ repository to all repositories that are using it.
 [7]: docs/gitlab-ci-deployment.md
 
 <!----------------------------------------------------------------------------->
-# Manifest pipeline
+## Manifest pipeline
 <!----------------------------------------------------------------------------->
 
 See this chapter for the pipeline runnning in the manifest repository to build
@@ -66,7 +66,7 @@ the images.
 [8]: docs/manifest-pipeline.md
 
 <!----------------------------------------------------------------------------->
-# Add new project to be handled by the pipeline
+## Add new project to be handled by the pipeline
 <!----------------------------------------------------------------------------->
 
 See this chapter for the steps needed to setup a new project using the pipeline.