Add some targets back in docker makefile

I now understand how they can be useful...

makefile

@@ -2,7 +2,7 @@ DOCKER_IMAGE := ghcr.io/hendricius/the-sourdough-framework
 DOCKER_CMD := docker run -it -v $(PWD):/opt/repo $(DOCKER_IMAGE) /bin/bash -c
 
 .PHONY: bake build_pdf build_docker_image push_docker_image validate website
-.PHONY: print_os_version start_shell printvars show_tools_version
+.PHONY: print_os_version start_shell printvars show_tools_version mrproper
 
 # Dockers targets
 build_docker_image:
@@ -17,12 +17,18 @@ push_docker_image: build_docker_image
 validate:
 	$(DOCKER_CMD) "cd /opt/repo/book && make -j build_serif_pdf build_ebook"
 
+build_pdf:
+	$(DOCKER_CMD)  "cd /opt/repo/book && make"
+
 bake:
-	$(DOCKER_CMD) "cd /opt/repo/book && make bake"
+	$(DOCKER_CMD) "cd /opt/repo/book && make -j bake"
 
 website:
 	$(DOCKER_CMD) "cd /opt/repo/book && make website"
 
+mrproper:
+	$(DOCKER_CMD) "cd /opt/repo/book && make mrproper"
+
 # Debug helpers
 show_tools_version:
 	$(DOCKER_CMD) "cd /opt/repo/book && make show_tools_version"