update help to include html_noapi target

docs/Makefile

@@ -19,14 +19,15 b' default: html'
 
 help:
 	@echo "Please use \`make <target>' where <target> is one of"
-	@echo "  html      to make standalone HTML files"
-	@echo "  pickle    to make pickle files (usable by e.g. sphinx-web)"
-	@echo "  htmlhelp  to make HTML files and a HTML help project"
-	@echo "  latex     to make LaTeX files, you can set PAPER=a4 or PAPER=letter"
-	@echo "  texinfo   to make Texinfo files"
-	@echo "  info      to make Texinfo files and run them through makeinfo"
-	@echo "  changes   to make an overview over all changed/added/deprecated items"
-	@echo "  linkcheck to check all external links for integrity"
+	@echo "  html        standalone HTML files"
+	@echo "  html_noapi  same as above, without the time consuming API docs"
+	@echo "  pickle      pickle files (usable by e.g. sphinx-web)"
+	@echo "  htmlhelp    HTML files and a HTML help project"
+	@echo "  latex       LaTeX files, you can set PAPER=a4 or PAPER=letter"
+	@echo "  texinfo     Texinfo files"
+	@echo "  info        Texinfo files and run them through makeinfo"
+	@echo "  changes     an overview over all changed/added/deprecated items"
+	@echo "  linkcheck   check all external links for integrity (takes a long time)"
 	@echo
 	@echo "Compound utility targets:"
 	@echo "pdf          latex and then runs the PDF generation"