Tweak jupyter appendix

Add extra 'sub' to each (sub)*section to give section to each notebook

Makefile

@@ -58,7 +58,11 @@ nb-appendix:
 define NOTEBOOK_TO_TEX_RULE
 $(1).tex: $(1).ipynb
 	jupyter nbconvert --to latex $(1).ipynb
-	sed -e '/\\documentclass/,/\\maketitle/d' -e '/\\end{document}/d' -i  $(1).tex
+	sed \
+	-e '/\\documentclass/,/\\maketitle/d' \
+	-e '/\\end{document}/d' \
+	-e 's;section{;subsection{;' \
+	-i  $(1).tex
 endef
 
 NOTEBOOKBASENAMES=$(basename $(wildcard **/*.ipynb))