Update welcome.html
update from lab
Merge branch 'master' of https://github.com/yishanhe/yishanhe.github.com

Conflicts:
	_includes/themes/twitter/welcome.html
	index.md
Merge branch 'master' of https://github.com/yishanhe/yishanhe.github.com
	_wiki_source/aiml.wiki
	wiki/aiml.html