Update new Arti documentation page with current logo and color
The new (& beautiful!) Arti documentation page needs to be updated with the current logo, and the hyperlink color to updated as well.
Logo: arti-straight-purple.png
#8E59FF
for the hyperlinks please!
For reference, approved Arti logos for use are here in the Brand and Operations folder under the UX Team folder: Nextcloud
Thanks! :)