appimage: install missing libsndio7.0 package

[benoit-pierre]

The sndio library is required for creating the appimage.

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This change is 

[benoit-pierre]

With koreader/koreader#11662 I can run ./kodev release appimage successfully.

Except I have to force the DOCKER variable to 1 in the Makefile, as the detection is not working. I just switched to rootless mode, so that might be the issue.

[Frenzie]

A quick search suggests you can detect Docker by the existence of /.dockerenv. I can confirm that works for me.

https://superuser.com/questions/1021834/what-are-dockerenv-and-dockerinit/1115029#1115029

But since it might change depending on the Docker version (and presumably Podman won't have a /.dockerenv) , I think we should simply add our own "yup, this is Docker" file to the image.

For detection perhaps we should still say if our_this_is_docker_file or /.dockerenv as a generic fallback in case someone uses their own maximalist development Docker image?

[benoit-pierre]

Or we could switch to a more simpler approach:

# Is fuse support available?
USE_FUSE ?= $(wildcard /dev/fuse)

Which works in Docker / Podman, and also provides an escape hatch (make USE_FUSE=, useful for testing).

[Frenzie]

Implemented in koreader/koreader#11669