Release docs

We want to make our docs widely accessible. From [this comment](https://github.com/cowprotocol/solana-programs/pull/81#discussion_r3671298109):

> would make sense to export the generated docs to a build archive. The archive could be loaded as is by many static hosting providers, like [cloudflare pages](https://developers.cloudflare.com/pages/get-started/direct-upload/#supported-file-types)