Remove old markdown notebooks from dev.-phase

[hsloot]

Related issues

None

Checklist

• [x] R CMD CHECK successful
• [x] tests included
• [x] documentation included or updated
• [x] commit messages follow commit guidelines

Optional, but recommended:

• [x] code passes lintr::lint_package() without errors

Description

Proposed changes:

• Remove old rmarkdown notebook used in the development phase of the package
• Update README reference

[codecov[bot]]

Codecov Report

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

Project coverage is 95.85%. Comparing base (09f775e) to head (9e679c1).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #115 +/- ## ======================================= Coverage 95.85% 95.85% ======================================= Files 46 46 Lines 1399 1399 ======================================= Hits 1341 1341 Misses 58 58 ```

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