document the highly advanced Makefile

Makefile

@@ -13,6 +13,11 @@ else
 endif
 
 $(OUT): README.adoc $(HEAD) $(FOOT) template_dir/*
+	@# --embedded + head/foot originally added to fix image height:
+	@# https://stackoverflow.com/questions/63464732/how-to-set-a-custom-image-height-for-an-image-in-asciidoctor
+	@#
+	@# --template-dir initially added for loading="lazy" on images and youtube iframes:
+	@# https://stackoverflow.com/questions/63917971/how-to-create-custom-html-output-for-an-existing-asciidoctor-asciidoc-macro
 	bundle exec asciidoctor \
 		$(MEDIA_CMD) \
 	  --embedded \