Added readme for generated demo to avoid confusion

Makefile

@@ -23,6 +23,8 @@ gh-pages: browserify demo
 	cp -r ./demo ./demo-web
 	cp ./dist/markdown-it.js ./demo-web
 	sed -i "s|../dist|.|" ./demo-web/index.html
+	cp ./support/demo_readme.md ./demo-web/README.md
+	touch ./demo-web/.nojekyll
 	cd ./demo-web \
 		&& git init . \
 		&& git add . \

support/demo_readme.md

@@ -0,0 +1,3 @@
+This repo is generated from __[markdown-it](https://github.com/markdown-it/markdown-it)__ by script.
+
+Please, use __[markdown-it](https://github.com/markdown-it)__ for all questions & PRs.