You must follow the conventional commits schema. Commits are linted and will fail if they are not following the schema. This helps to be consistent across developers and makes semantic-release possible.
If you change the README.md, use docs! to trigger a breaking change
(increases major version) to make the change visible at the npm registry.
You don't need to take care of any library building when you are finished. Releases are done automatically by semantic-release. You must follow the given commit schema (see Conventional commits) to trigger an automatic release with the correct versioning.