Update help command in makefile
diff --git a/Makefile b/Makefile
index f38e383..e1f9dec 100644
--- a/Makefile
+++ b/Makefile
@@ -40,7 +40,8 @@
 
 help:
 	@echo "Please use \`make <target>' where <target> is one of"
-	@echo "  html       to make standalone HTML files"
+	@echo "  doc-html       to make standalone HTML files"
+	@echo "  doc-pdf        to make standalone PDF files"
 
 clean:
 	rm -rf $(BUILDDIR)/*
@@ -104,4 +105,4 @@
 	$(SPHINXBUILD) -b latex $(ALLSPHINXOPTS) source/manual $(BUILDDIR)/protocol/pdf
 	@echo "Running LaTeX files through pdflatex..."
 	$(MAKE) -C $(BUILDDIR)/protocol/pdf all-pdf
-	@echo "pdflatex finished; the PDF files are in $(BUILDDIR)/protocol/pdf."
\ No newline at end of file
+	@echo "pdflatex finished; the PDF files are in $(BUILDDIR)/protocol/pdf."