Improved use instructions, Steam Sniper and Proton-GE version bumps, added .desktop file, handling .CLIP files from file managers

[exentio]

Hello! It's technically not good practice to push all these changes in a single pull request, but I'm porting the changes after I made them on my system, and considering the kind of repo I think we're can get away with this hehe

My changes are:

• Added a missing shebang to the csp-linux script.
• Fixed the OS detection, OpenSUSE outputs linux instead of linux-gnu, and the script now accepts both.
• Specified in the readme that, in order to launch Clip Studio Paint with the csp-linux command, the user needs to be in the folder of the repo, or otherwise add a path with the script to their PATH environment variable.
• Bumped versions for the Steam Sniper container runtime and for Proton-GE to their current latest versions, they may have bug fixes and performance improvements, and they appear to work fine on both OpenSUSE Tumbleweed and Arch Linux.
• Added a .desktop file so that desktop environments can find and launch CSP from their application launchers.
• Changed the csp-linux script so it can handle files as arguments and open them. This added an optional dependency to wine/winepath, without it the script will still run.
• Added info regarding a thumbnail plugin for KDE in the readme.
• Replaced the acknowledgment at the end with just "Made with love", since this repo has received many crucial contributions from other people before me and it wouldn't be fair to have a single acknowledgment, while updating it to add new names every time would be a pain. I hope you won't mind!

[exentio]

Oh, and I just thought that it'd be a good idea to remove the .desktop file during the uninstall. I'll add it tomorrow, or you can add it yourself if you merge the PR in the meantime