Improve reader guidance on ["landing page"](https://specs.anoma.net/latest/index.html)

[heindel]

This issue concerns all versions of Anoma. Righ now, the "next" button refers to the changelog, which may not be the most interesting point to dig deeper into the subject matter.

There are two orthogonal ways to improve this:

• add a short "synopsis" after the current description of Anoma that

  • concerns the current version
  • gives some concrete pointers, e.g., highlight the (1-3) MVPs of the current version

• make Next point to the introduction