AppImage: compile Python with libreadline-dev

TODO.md

@@ -2,7 +2,7 @@
 
 ## Before release
 
-- readline
+- Debug mode always on, but prevent pdb if no terminal
 - Add Gentoo instructions
 - Finish the README.md
 - Build final AppImage and test media opening

build-appimage.sh

@@ -75,7 +75,7 @@ install_apt_packages() {
         libglfw3-dev libgles2-mesa-dev libjpeg-turbo8-dev zlib1g-dev \
         libtiff5-dev liblcms2-dev libwebp-dev  libopenjp2-7-dev libssl-dev \
         python3-dev python3-setuptools python3-pip libgdbm-dev libc6-dev \
-        zlib1g-dev libsqlite3-dev libffi-dev openssl \
+        zlib1g-dev libsqlite3-dev libffi-dev openssl libreadline-dev \
         desktop-file-utils  # for appimage-lint.sh
 
     /usr/sbin/update-ccache-symlinks