chore: add volta as prerequisite (#88)

* chore: add volta as prerequisite

* chore: explain why

README.md

@@ -7,6 +7,7 @@ Send emails to Cloudflare and forward them to different channels using an email
 #### Prerequisites
 
 - Cloudflare [account](https://dash.cloudflare.com/sign-up) (free)
+- [Volta](https://volta.sh/) installed (for managing correct Node and Yarn versions)
 - Wrangler installed [globally](https://developers.cloudflare.com/workers/wrangler/install-and-update/#install-wrangler-globally)
 
 #### Install dependencies