Document various runtimes (#4536)

Co-authored-by: Xingyao Wang <xingyao@all-hands.dev>

containers/app/Dockerfile

@@ -41,6 +41,7 @@ ENV SANDBOX_LOCAL_RUNTIME_URL=http://host.docker.internal
 ENV USE_HOST_NETWORK=false
 ENV WORKSPACE_BASE=/opt/workspace_base
 ENV OPENHANDS_BUILD_VERSION=$OPENHANDS_BUILD_VERSION
+ENV SANDBOX_USER_ID=0
 RUN mkdir -p $WORKSPACE_BASE
 
 RUN apt-get update -y \

containers/app/entrypoint.sh

@@ -18,6 +18,11 @@ if [ -z "$SANDBOX_USER_ID" ]; then
   exit 1
 fi
 
+if [ -z "$WORKSPACE_MOUNT_PATH" ]; then
+  # This is set to /opt/workspace in the Dockerfile. But if the user isn't mounting, we want to unset it so that OpenHands doesn't mount at all
+  unset WORKSPACE_BASE
+fi
+
 if [[ "$SANDBOX_USER_ID" -eq 0 ]]; then
   echo "Running OpenHands as root"
   export RUN_AS_OPENHANDS=false