Update installation.rst with download link
Why this change?
I wanted to install the app image. But for the life of me, after searching, I could not find the Download link? I went to the forums and asked a question.
Somehow I stumbled on the Krita website and got the download - but - I resolved to get a KDE login and submit a PR to the documentation. Perhaps there are others who face similar issues with the app image? I could not find the link