added example shell from bwrap git repo

bubblewrap/shell.sh

+#!/usr/bin/env bash
+#
+## Shell example modified to get stub for sandboxing cli tools
+##
+## https://github.com/containers/bubblewrap/blob/main/demos/bubblewrap-shell.sh
+#
+# Use bubblewrap to run /bin/sh reusing the host OS binaries (/usr), but with
+# separate /tmp, /home, /var, /run, and /etc. For /etc we just inherit the
+# host's resolv.conf, and set up "stub" passwd/group files.  Not sharing
+# /home for example is intentional.  If you wanted to, you could design
+# a bwrap-using program that shared individual parts of /home, perhaps
+# public content.
+#
+# Another way to build on this example is to remove --share-net to disable
+# networking.
+set -euo pipefail
+exec bwrap --ro-bind /usr /usr \
+      --dir /tmp \
+      --dir /var \
+      --symlink ../tmp var/tmp \
+      --proc /proc \
+      --dev /dev \
+      --ro-bind /etc/resolv.conf /etc/resolv.conf \
+      --symlink usr/lib /lib \
+      --symlink usr/lib64 /lib64 \
+      --symlink usr/bin /bin \
+      --symlink usr/sbin /sbin \
+      --chdir / \
+      --unshare-all \
+      --share-net \
+      --die-with-parent \
+      --dir /run/user/$(id -u) \
+      --setenv XDG_RUNTIME_DIR "/run/user/`id -u`" \
+      --setenv PS1 "bwrap-demo$ " \
+      --file 11 /etc/passwd \
+      --file 12 /etc/group \
+      /bin/sh) \
+    11< <(getent passwd $UID 65534) \
+    12< <(getent group $(id -g) 65534)