add "git show" to display HTML

Author: William Grant

docs/Makefile

@@ -17,7 +17,7 @@ help:
 
 show:
 	@echo "Showing generated html"
-
+	@python -c "import webbrowser; webbrowser.open_new_tab('file://$(PWD)/$(BUILDDIR)/html/index.html')"
 
 # Catch-all target: route all unknown targets to Sphinx using the new
 # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).