Fix small typo in the readme

[nikosbosse]

Description

This PR fixes two small issues in the Readme:

• The readme currently uses head(data, 2) to print the first two rows of a forecast object. This means that the forecast object fails validation (as it only has two rows with NA values left. This PR changes head(data, 2) to print(data, 2) which solves the problem.
• The link to the revised paper should belong to "revised version" not "updated version". I slightly adapted the link.

Checklist

• [ ] My PR is based on a package issue and I have explicitly linked it.
• [ ] I have included the target issue or issues in the PR title as follows: issue-number: PR title
• [ ] I have tested my changes locally.
• [ ] I have added or updated unit tests where necessary.
• [ ] I have updated the documentation if required.
• [ ] I have built the package locally and run rebuilt docs using roxygen2.
• [ ] My code follows the established coding standards and I have run lintr::lint_package() to check for style issues introduced by my changes.
• [ ] I have added a news item linked to this PR.
• [ ] I have reviewed CI checks for this PR and addressed them as far as I am able.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.36%. Comparing base (1a51fa8) to head (a78b0ab).

:exclamation: Current head a78b0ab differs from pull request most recent head 390db24. Consider uploading reports for the commit 390db24 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #760 +/- ## ======================================= Coverage 95.36% 95.36% ======================================= Files 21 21 Lines 1617 1617 ======================================= Hits 1542 1542 Misses 75 75 ```

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