Until Executed vs Unique Until And While Executing is confusing in README

[rafaelsales]

Still having hard time to see difference between Until Executed vs Unique Until And While Executing.

Text has some typos that might be making harder to understand as well.

For the one who implemented, it might be easy to understand though. If one could explain better here I could even try to revisit the README to make it easier to understand.

Thanks

[mhenrixon]

Feel free to provide a pull request with the typos fixed.

[mhenrixon]

Means the job is unique in two ways but only one at the time.