Update README (#97)

Author: malewis5

.changeset/violet-memes-say.md

@@ -0,0 +1,5 @@
+---
+"@vercel/slack-bolt": patch
+---
+
+Add badges to README

packages/slack-bolt/README.md

@@ -1,5 +1,8 @@
 # @vercel/slack-bolt
 
+[![npm version](https://img.shields.io/npm/v/%40vercel%2Fslack-bolt)](https://www.npmjs.com/package/@vercel/slack-bolt)
+[![npm downloads](https://img.shields.io/npm/dm/%40vercel%2Fslack-bolt?label=downloads)](https://www.npmjs.com/package/@vercel/slack-bolt)
+
 A custom [Slack Bolt](https://slack.dev/bolt-js/) receiver built for Vercel's [Fluid Compute](https://vercel.com/docs/fluid-compute).
 
 ## Getting Started