cookbook/container: example of building+running docker containers.

This got... long... and complicated.  But I think it's a really good
demonstration of getting redo to do complicated things elegantly.  At
least, I hope it is.

docs/cookbook/container/libs.fs.do

@@ -0,0 +1,21 @@
+exec >&2
+
+fs=${1%.fs}
+redo-ifchange simple.fs
+
+rm -rf "$fs"
+cp -a simple/. "$fs"
+
+for full in "$fs"/bin/*; do
+	if [ -x "$full" ]; then
+		ldd "$full" | while read a b c junk; do
+			[ "$b" = "=>" ] && a=$c
+			if [ -e "$a" ]; then
+				mkdir -p "$fs/lib" "$fs/$(dirname "$a")"
+				cp -f "$a" "$fs/$a"
+			fi
+		done
+	fi
+done
+
+redo-ifchange "$fs/bin/sh"