Update README.md with strike fragment
Update README.md with strike fragment

the strike type fragment was un-documented, so I stuck a mention of it in with the others.
rbtcollins/reveal.js,dbs/reveal.js,tehfedaykin/10CommandmentsofCommunityOrganizing,rbtcollins/reveal.js,lvh/reveal.js,Jean85/reveal.js,jayramj/agile-retro,10xEngineer/reveal.js,tehfedaykin/10CommandmentsofCommunityOrganizing,hakimel/reveal.js,hakimel/reveal.js,siddhartha-gadgil/presentations,Jean85/reveal.js,lecovi/reveal.js,10xEngineer/reveal.js,maximesinclair/presentations,seefood/DIYHolidays,maximesinclair/presentations,kenkunz/js-crash-course,lvh/reveal.js,lecovi/reveal.js,lecovi/reveal.js,seefood/DIYHolidays,rbtcollins/reveal.js,rbtcollins/reveal.js,siddhartha-gadgil/presentations,dbs/reveal.js,jayramj/agile-retro,siddhartha-gadgil/presentations,kenkunz/js-crash-course,rbtcollins/reveal.js,rbtcollins/reveal.js