feat: new readme for 4.0 (#284)

* feat: new readme for 4.0

* fix: improved wording

* fix: based on kyles suggestions

* fix: remove random new line

* fix: next.js

* fix: introduce lower level fns first, illustrate mapping of higher level fns

* feat: added computeDigestMultibase

* fix: header

* fix: update to reflect code changes

* fix: package exports really helps most when treeshaking is not possible