Update AttachFile jelly tag documentation

The AttachFile jelly tag documentation needs update as it has a new parameter called created as part of JRA-13654

http://www.atlassian.com/software/jira/docs/latest/jelly.html#AttachFile

The changes needed are:

• Add new optional attribute called created (Please see CreateIssue's created attribute entry
• Note that key & filepath attributes are required
• Note that option & created attributes are optional
• Note in the option attributes description that if the option is empty string ("") or not provided it will default to "add"