Add "Demo" subheading under "Features" in README.md
Add "Demo" subheading under "Features" in README.md

The link to real world example at Pantsu.cat is not semantically a
feature, but its own demonstration. Adding a subheader for the example
increases semantics further, and makes it easier to find.

pomf/pomf,alucard0134/Pomf,ewhal/gpomf,alucard0134/Pomf,pomf/pomf,pomf/pomf-php,alucard0134/Pomf