Example on how to use this.
Imagine you want to use the Leafpad text editor, but carry its settings around with the executable.
You can do the following:
# Download Leafpad AppImage and make it executable
wget -c "https://bintray.com/probono/AppImages/download_file?file_path=Leafpad-0.8.18.1.glibc2.4-x86_64.AppImage" -O Leafpad-0.8.18.1.glibc2.4-x86_64.AppImage
chmod a+x Leafpad-0.8.18.1.glibc2.4-x86_64.AppImage
# Create a directory with the same name as the AppImage plus the ".config" extension
# in the same directory as the AppImage
# Run Leafpad, change some setting (e.g., change the default font size)
# then close Leafpad
# Now, check where the settings were written:
linux@linux:~> find Leafpad-0.8.18.1.glibc2.4-x86_64.AppImage.config
Note that the file
leafpadrc was written in the directory we have created before.