clarify pandoc version message

Makefile

@@ -3,7 +3,7 @@ PDF=$(SRC:.md=.pdf)
 HTML=$(SRC:.md=.html)
 
 all: ffv1.html ffv1.pdf
-	@echo "Propering PDF and HTML rendering has been tested with requires pandoc version 1.13.2.1 and higher."
+	@echo "PDF and HTML rendering has been tested with pandoc version 1.13.2.1, some older versions are known to produce very poor output, please ensure your pandoc is recent enough."
 
 ffv1.html: ffv1.md
 	pandoc --toc --mathml -s --number-sections  -c "http://elyxer.nongnu.org/lyx.css" -o "$@" "$<"