packaged appimages for aur

[Ckath]

created chatterino2-appimage and chatterino2-nightly-appimage according to the discussion in #2736

added the same co-maintainers as the last one(including the ci), let me know if any one else needs to be added.

for the integration:

• the regular appimage needs pkgver and the md5sums(generated with makepkg -g) updated every release
• the nightly is done with a pkgver of the current date(can use anything really) and a static nightly-build url, bumping pkgver alone will be enough as md5sums are also skipped

if anything about these looks wrong(not very familiar with appimages myself) also feel free to let me know, this is how I saw most other -appimage packages done and it seemed logical to me.

[Ckath]

what I run manually now for updating these, not sure if they'd translate to ci and I'm too lazy to look at it tbh

chatterino2-appimage

sed -i "s/pkgver=.*/pkgver=$newver/" PKGBUILD
sed -i "s/md5sums.*/$(makepkg -g)/" PKGBUILD
makepkg --printsrcinfo > .SRCINFO
rm -rf Chatterino-x86_64.AppImage src
git add PKGBUILD .SRCINFO
git commit -m "update to $newver"

chatterino2-nightly-appimage

sed -i "s/pkgver=.*/pkgver=$(date +'%Y.%m.%d')/" PKGBUILD
makepkg --printsrcinfo > .SRCINFO
git add PKGBUILD .SRCINFO
git commit -m "version bump"