Adding info about holidats (#9930)

Update rule.md

rules/check-the-calendar-when-planning-an-event/rule.md

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 When planning an event, everything revolves around the date so it’s vital to be sure there are no potential clashes or conflicts. We recommend using [a SharePoint calendar](http://www.ssw.com.au/ssw/Events/Events.aspx), to let employees and the public keep up to date with what your organisation is holding or attending. It is best to have more than 1 date in mind for your event when you start planning, as this affords you flexibility if your first choice of date won’t work out.
 
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 Be sure to check the dates and times of other events happening for that day. Depending on your event, it might also be worth looking for events on either side of your date, in case one of the events will be especially exhausting or costly, as this is likely to make people less interested in attending a second event right away.
 
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+Note: Events close to major holidays, i.e. Christmas, will often draw a smaller crowd and are more likely to need to be postponed