Link to the github-pages generated documentation

To update the documentation, do the following:

  	# delete current documentation
	pushd doc/html
	rm -rf $PWD/*
	# clone into current directory, checkout gh-pages
	git clone git@github.com:libratbag/libratbag .
	git checkout -b gh-pages
	# delete master branch so we don't accidentally push that one
	git branch -d master
	# return to main, generate docs
	popd
	make
	# commit updated docs, push
	pushd doc/html
	git commit -asm "Updated documentation"
	git push origin gh-pages
	popd

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

README.md

@@ -7,6 +7,13 @@ libratbag is a configuration library for gaming mice. It provides a generic
 way to access the various features exposed by these mice and abstracts away
 hardware-specific and kernel-specific quirks.
 
+Documentation
+-------------
+
+API documentation is available here:
+
+	http://libratbag.github.io/libratbag/
+
 Architecture
 ------------