Bump version, add docker pulls to readme

Author: antonym

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.20.3
+FROM alpine:3.21.2
 
 # set version label
 ARG BUILD_DATE

README.md

@@ -3,6 +3,7 @@
 [![Release Status](https://github.com/netbootxyz/docker-netbootxyz/actions/workflows/release.yml/badge.svg)](https://github.com/netbootxyz/docker-netbootxyz/actions/workflows/release.yml)
 [![Discord](https://img.shields.io/discord/425186187368595466)](https://discord.gg/An6PA2a)
 ![GitHub tag (latest by date)](https://img.shields.io/github/v/tag/netbootxyz/docker-netbootxyz)
+![Docker Pulls](https://img.shields.io/docker/pulls/netbootxyz/netbootxyz)
 
 ## Overview