"VOLUME /books" was missing from Dockerfile

[salfter]

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:

The Dockerfile is missing a VOLUME /books declaration, so you can't mount a library against it.

Benefits of this PR and context:

As it's currently shipping, the container doesn't work because it can't access libraries.

How Has This Been Tested?

In my docker-compose.yml, I replaced image: lscr.io/linuxserver/docker-readarr with build: docker-readarr, built a new container, and brought it up. My books are now visible within the container.

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[j0nnymoe]

This is not needed. We only add the /config volume as part of our containers docker files as it's the main one that's required. Outside of that, users are welcome to add whatever folder's they need via bind mounts.

For Example: https://github.com/linuxserver/docker-sonarr/blob/5f634a338cbf0c28fd4373894ac04dfed285f292/Dockerfile#L50 We don't have /tv in sonarr.

[LinuxServer-CI]

I am a bot, here are the test results for this PR:
https://ci-tests.linuxserver.io/lspipepr/readarr/develop-0.4.4.2686-pkg-0dc06621-dev-236ddc587fa33ca63036ea8eba14ad4a52c274b6-pr-41/index.html
https://ci-tests.linuxserver.io/lspipepr/readarr/develop-0.4.4.2686-pkg-0dc06621-dev-236ddc587fa33ca63036ea8eba14ad4a52c274b6-pr-41/shellcheck-result.xml

Tag	Passed
amd64-develop-0.4.4.2686-pkg-0dc06621-dev-236ddc587fa33ca63036ea8eba14ad4a52c274b6-pr-41	✅
arm64v8-develop-0.4.4.2686-pkg-0dc06621-dev-236ddc587fa33ca63036ea8eba14ad4a52c274b6-pr-41	✅

[salfter]

This is not needed. We only add the /config volume as part of our containers docker files as it's the main one that's required. Outside of that, users are welcome to add whatever folder's they need via bind mounts.

For Example: https://github.com/linuxserver/docker-sonarr/blob/5f634a338cbf0c28fd4373894ac04dfed285f292/Dockerfile#L50 We don't have /tv in sonarr.

Noted, and Sonarr does work properly that way (I have /mnt/storage/tv-shows mounted to /tv). However, a similar declaration wasn't working with Readarr for /books (though it was working for /downloads), at least not when using Docker Compose. echo ls /books | docker run -i --rm --entrypoint ash -v /mnt/storage/books/Calibre\ Library/:/books lscr.io/linuxserver/readarr:develop produced the expected results, however.

Just tried again with the published container and Docker Compose, and I'll be damned if it isn't working properly now. I don't know why it wasn't working earlier.