Added the missing UMASK section.

[uhop]

See #272

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

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Description:

Trivial 3-line section to set UMASK to settings.json as per the current documentation.

Benefits of this PR and context:

It fixes the filed bug, which clearly annoys people (including me).

How Has This Been Tested?

I ran it and saw the change in /config/settings.json.

Source / References:

The existing doc:

docker-transmission/README.md

Line 177 in a63cd60

## Umask for running applications

The bug: #272

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https://ci-tests.linuxserver.io/lspipepr/transmission/4.0.6-r0-pkg-6730fbea-dev-20cf81ec2e49fec458e140de6b32f0d733094c47-pr-288/shellcheck-result.xml

Tag	Passed
amd64-4.0.6-r0-pkg-6730fbea-dev-20cf81ec2e49fec458e140de6b32f0d733094c47-pr-288	✅
arm64v8-4.0.6-r0-pkg-6730fbea-dev-20cf81ec2e49fec458e140de6b32f0d733094c47-pr-288	✅

[LinuxServer-CI]

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https://ci-tests.linuxserver.io/lspipepr/transmission/4.0.6-r0-pkg-f68ac517-dev-356173a6975a42c4e5ed422e07f0af9baf10e8a6-pr-288/index.html
https://ci-tests.linuxserver.io/lspipepr/transmission/4.0.6-r0-pkg-f68ac517-dev-356173a6975a42c4e5ed422e07f0af9baf10e8a6-pr-288/shellcheck-result.xml

Tag	Passed
amd64-4.0.6-r0-pkg-f68ac517-dev-356173a6975a42c4e5ed422e07f0af9baf10e8a6-pr-288	✅
arm64v8-4.0.6-r0-pkg-f68ac517-dev-356173a6975a42c4e5ed422e07f0af9baf10e8a6-pr-288	✅

[LinuxServer-CI]

I am a bot, here are the test results for this PR:
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https://ci-tests.linuxserver.io/lspipepr/transmission/4.0.6-r0-pkg-2cb64b31-dev-f5cd1a2f5fbf0f94c760cef575dbcb3e1410e1fb-pr-288/shellcheck-result.xml

Tag	Passed
amd64-4.0.6-r0-pkg-2cb64b31-dev-f5cd1a2f5fbf0f94c760cef575dbcb3e1410e1fb-pr-288	✅
arm64v8-4.0.6-r0-pkg-2cb64b31-dev-f5cd1a2f5fbf0f94c760cef575dbcb3e1410e1fb-pr-288	✅

[drizuid]

im tentatively on board with this fix, i forgot about this issue, tbh. Howeever, i have some concerns about weird shit qnap/synology/unraid might do in terms of umask.. i don't think it should cause a problem, but I will ping the rest of the team to give thoughts before merge.