Add support for rootless docker

Dockerfile

@@ -2,4 +2,8 @@ ARG SDK_VERSION
 FROM k8r.eu/justjanne/android-sdk:$SDK_VERSION
 
 RUN apt-get --quiet update --yes && \
-    apt-get --quiet install --yes python3 python3-lxml
+    apt-get --quiet install --yes python3 python3-lxml uidmap
+
+RUN useradd -r -u 1001 -g builduser builduser
+USER builduser
+RUN curl -fsSL https://get.docker.com/rootless | sh