README.md: Use 'written' instead of 'wrote'

The use of written instead of wrote is important in modern english.
It has several implications:

- User having to write written instead of wrote
- The case where the user has to write instead of writting
- Any other case

Therefore it is best to use written instead of wrote to avoid
cases where it would have been written as wrote.
Merge pull request #1 from crumblingstatue/written_instead_of_wrote_feature_branch

README.md: Use 'written' instead of 'wrote'