[BUG] build_appimage.sh calls appimagetool without checking for its presence

[Beethoven-n]

i discussed this on the discord, but that's getting buried instantly because it's discord, lol.

a bit of a rough edge is that the build script for the appimage doesn't actually check for appimagetool's presence in the repo, leading to a simple "no file or directory" error:

./build_appimage.sh: line 139: ./appimagetool: No such file or directory

you have two options:

• lean on the user's existing installation of appimagetool
• pull from latest here: https://github.com/AppImage/appimagetool/releases/download/continuous/appimagetool-x86_64.AppImage

telescope/build_appimage.sh

Line 139 in e33764c

./appimagetool "Telescope.AppDir" Telescope-x86_64.AppImage

which would be the preferable situation?