docs/Makefile.am: add build rules for audiowmark.pdf and audiowmark.html

Signed-off-by: Tim Janik <timj@gnu.org>

docs/Makefile.am

+# docs/Makefile.am
+
+doc_DATA  = audiowmark.pdf audiowmark.html
+
+GRAPHVIZ_PY = graphviz.py
+
+audiowmark.pdf: audiowmark.md $(GRAPHVIZ_PY)
+	pandoc -F $(GRAPHVIZ_PY) -V papersize:a4 -V geometry:margin=2cm $< -o $@
+
+audiowmark.html: audiowmark.md $(GRAPHVIZ_PY)
+	pandoc -F $(GRAPHVIZ_PY) $< -o $@
+
+# DEPS: apt install -y python3-pygraphviz python3-pandocfilters
+
+clean:
+	rm -f -r ../docs/graphviz-images/
+	rm -f $(doc_DATA)
+