docker: run as non-root user in containers using this image

.docker/Dockerfile

@@ -23,6 +23,10 @@ RUN mkdir -p /var/cache/distfiles/git3-src && chown portage:portage /var/cache/d
 
 RUN emerge =dev-build/meson-9999
 
+RUN useradd -m gentooligan
+
+USER gentooligan
+
 WORKDIR /workspace
 
 ENTRYPOINT /bin/bash