Update readme to point to x(ht)ml tag
Update readme to point to x(ht)ml tag

Per https://github.com/tmpvar/jsdom/issues/885#issuecomment-230127793.
snuggs/jsdom,tmpvar/jsdom,Zirro/jsdom,tmpvar/jsdom,mzgol/jsdom,mzgol/jsdom,snuggs/jsdom,mzgol/jsdom,Zirro/jsdom