add Dockerfile

Dockerfile

+FROM registry.gitlab.com/islandoftex/images/texlive:latest
+
+ARG USERNAME="vscode"
+ARG USER_UID="1000"
+ARG USER_GID=${USER_UID}
+ARG WORKSPACE="/workdir"
+
+RUN groupadd --gid ${USER_GID} ${USERNAME} \
+    && useradd --uid ${USER_UID} --gid ${USER_GID} -m ${USERNAME} \
+    && mkdir -p ${WORKSPACE}
+
+USER $USERNAME
+WORKDIR ${WORKSPACE}