Collecting Plasma features

[Nate Graham]

Hello folks!

I've started describing Plasma features and other notable changes on 
https://community.kde.org/Plasma/Plasma_6#User-facing_changes. This 
helps the Promo team write Plasma release announcements.

I've already done this for 6.2 and grouped things into high-level 
topics; see https://community.kde.org/Plasma/Plasma_6#Plasma_6.2

Once we branch in a few days, the merge window will open for 6.3. When 
you merge something user-facing and noteworthy, please write about it on 
https://community.kde.org/Plasma/Plasma_6#Plasma_6.3!

Thanks everyone!

Nate