Fix typos in getting started section of the documentation

[pietsjoh]

Description

Fixes some typos in the getting started section of the documentation.

There is also a broken link (line 54, favourite package). After a brief look at the documentation of pytorch lightning, I am not really sure with that should be replaced. So feel free to add a commit with the corrected link. Otherwise I could also open an issue for that. Just let me know :)

Checklist

• Linked issues (if existing)
• Amended changelog for large changes (and added myself there as contributor)
• Added/modified tests
• Used pre-commit hooks when committing to ensure that code is compliant with hooks. Install hooks with pre-commit install.
  To run hooks independent of commit, execute pre-commit run --all-files

Make sure to have fun coding!