Assorted changes: community and l10n content
- Add Krita Artists to community page
- Add links to https://community.kde.org/Get_Involved/translation regarding l10n
- Some capitalization fixes
I don't know what else to write for the Krita Artists section. Please feel free to add to it or revise it.
I also don't know if any of these changes shall be cherry-picked to 5.0.