Update CONTRIBUTING.md

rename appimagetool after download and move

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: NeuralFault

CONTRIBUTING.md

@@ -24,8 +24,8 @@ sudo apt-get -y install fuse3
 # Download appimagetool (uses static type2-runtime; end users still need
 # fusermount or fusermount3 setuid helper on their system, or can use
 # --appimage-extract-and-run as a fallback)
-sudo wget -q https://github.com/AppImage/appimagetool/releases/download/continuous/appimagetool-x86_64.AppImage -O /usr/local/bin/appimagetool-x86_64.AppImage
-sudo chmod +x /usr/local/bin/appimagetool-x86_64.AppImage
+sudo wget -q https://github.com/AppImage/appimagetool/releases/download/continuous/appimagetool-x86_64.AppImage -O /usr/local/bin/appimagetool
+sudo chmod +x /usr/local/bin/appimagetool
 dotnet tool install -g KuiperZone.PupNet --version 1.9.1
 pupnet -r linux-x64 -c Release --kind appimage --app-version $RELEASE_VERSION --clean
 ```