Add a subscription input on the home page

## Context

We currently have two ways to allow our users follow the latest changes:

1. Through Twitter: https://twitter.com/stormkitio
2. Through Discord: https://discord.com/invite/6yQWhyY

Some users, however, may want to subscribe to our mailing list to get notified about significant changes. A subscription input on the home page could be useful for this matter. 