added siunitx example

documents/si-units/Makefile

@@ -0,0 +1,7 @@
+SOURCE = si-units
+make:
+	pdflatex $(SOURCE).tex -output-format=pdf
+	make clean
+
+clean:
+	rm -rf  $(TARGET) *.class *.html *.log *.aux *.out

documents/si-units/README.md

@@ -0,0 +1,2 @@
+Read the [manual](ftp://ftp.tex.ac.uk/tex-archive/macros/latex/exptl/siunitx/siunitx.pdf)
+for more information how `siunitx` works.