Urgent small fixes in the Dockerfile and Compose configs (#972)

* Freeze UID and GID for the `photoview` user inside the image; added alternative permission configs description to the Readme and Makefile (as a comment); switched the default tag in the compose from `2` to `master`, as this is the most common user misunderstanding according to the issues and Discord questions

* Revert back to the tag `2` with the assumption of the release happening soon

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Co-authored-by: Konstantin Koval

Dockerfile

@@ -62,7 +62,8 @@ ARG TARGETPLATFORM
 # See for details: https://github.com/hadolint/hadolint/wiki/DL4006
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 # Create a user to run Photoview server
-RUN useradd -r -U -m photoview \
+RUN groupadd -g 999 photoview \
+  && useradd -r -u 999 -g photoview -m photoview \
   # Required dependencies
   && apt-get update \
   && apt-get install -y curl gnupg gpg libdlib19.1 ffmpeg exiftool libheif1 sqlite3 \