GPLv3 licensing of elementary icons

Hey there,

Have been following helloSystem since it showed up on Lobste.rs a few months ago and happy to see it coming along. :)

Something I noticed in the new website and double-checked here, it seems like you're using some of the elementary icons without the license attached. I'm not sure how many there are, but the "big" one seems to be:

- https://github.com/helloSystem/Utilities/blob/master/Utilities/Calendar.app/Resources/Calendar.png
- https://github.com/elementary/icons/blob/master/apps/128/office-calendar.svg

I ran this by the elementary folks on their Slack and as more of an FYI, these icons are under the GPLv3 license which is available [here](https://github.com/elementary/icons/blob/master/COPYING) and should be reproduced with usage of the icons.

If you have any questions cc @danrabbit

Thanks!