Use tmpfs for /tmp

This is relevant when docker is used as container runtime as it does not
set /tmp as tmpfs. With podman /tmp is mounted as tmpfs due to
`--read-only-tmpfs` (enabled by default).

Fixes: #3463

docs/setup/install/container.md

@@ -34,6 +34,7 @@ Registry](https://github.com/juanfont/headscale/pkgs/container/headscale). The c
       --name headscale \
       --detach \
       --read-only \
+      --tmpfs /tmp \
       --tmpfs /var/run/headscale \
       --volume "$(pwd)/config:/etc/headscale:ro" \
       --volume "$(pwd)/lib:/var/lib/headscale" \

docs/setup/install/main.md

@@ -29,6 +29,7 @@ docker run \
   --name headscale \
   --detach \
   --read-only \
+  --tmpfs /tmp \
   --tmpfs /var/run/headscale \
   --volume "$(pwd)/config:/etc/headscale:ro" \
   --volume "$(pwd)/lib:/var/lib/headscale" \