Add docker badge

Readme.md

@@ -5,6 +5,7 @@
 [![Coverage](https://img.shields.io/codecov/c/github/Tyrrrz/DiscordChatExporter/master)](https://codecov.io/gh/Tyrrrz/DiscordChatExporter)
 [![Release](https://img.shields.io/github/release/Tyrrrz/DiscordChatExporter.svg)](https://github.com/Tyrrrz/DiscordChatExporter/releases)
 [![Downloads](https://img.shields.io/github/downloads/Tyrrrz/DiscordChatExporter/total.svg)](https://github.com/Tyrrrz/DiscordChatExporter/releases)
+[![Pulls](https://img.shields.io/docker/pulls/tyrrrz/discordchatexporter)](https://hub.docker.com/r/tyrrrz/discordchatexporter)
 [![Discord](https://img.shields.io/discord/869237470565392384?label=discord)](https://discord.gg/2SUWKFnHSm)
 [![Donate](https://img.shields.io/badge/donate-$$$-8a2be2.svg)](https://tyrrrz.me/donate)
 [![Fuck Russia](https://img.shields.io/badge/fuck-russia-e4181c.svg?labelColor=000000)](https://twitter.com/tyrrrz/status/1495972128977571848)