Completed README.md with explanation about what we want
Some changes after comments in pull request

- Sentence rewording
- Changed step wording for coherence
- Changed a constant name for coherence
Some more changes after pull request comments.

- Reworded the first step to make it clearer
- Added a sentence to clarify how they need to send us the results
Merge pull request #2 from albertpastrana/exercise_description

Completed README.md with explanation about what we want