fixup: replace text with images

Makefile

@@ -12,6 +12,8 @@ presentation=\
 
 versionsgraphen=\
 	grafiken/example-graph.pdf \
+	grafiken/example-graph-hl-branch.pdf \
+	grafiken/example-graph-hl-merge.pdf \
 	grafiken/ex1-graph.pdf \
 	grafiken/ex1-graph-precommit.pdf \
 	grafiken/ex2-graph-precommit.pdf \
@@ -30,7 +32,8 @@ grafiken=\
 	$(versionsgraphen) \
 	grafiken/github-workflow.pdf \
 	grafiken/github-actions.pdf \
-	grafiken/git-object.pdf
+	grafiken/git-object.pdf \
+	grafiken/concept-overview.pdf
 
 bilder=\
 	presentation/github-repo.png \