Add container-pids tool

tools/container-pids.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+# https://unix.stackexchange.com/a/299198
+descendent_pids() {
+    pids=$(pgrep -P $1)
+    echo $pids
+    for pid in $pids; do
+        descendent_pids $pid
+    done
+}
+
+build_pid=$(pgrep -f '\./build')
+echo $build_pid
+descendent_pids $build_pid