included better link to operations with support for LOCK=NONE

Optionally you could also link to http://www.tocker.ca/2013/11/05/a-closer-look-at-online-ddl-in-mysql-5.6.html, but I thought it would be better to point to the source.
Merge pull request #1 from morgo/patch-1

included better link to operations with support for LOCK=NONE