Update README.md
more details on arguments with default values
Merge branch 'master' of github.com:lewagon/promo-4-challenges
Allow students to use return
Merge pull request #7 from lewagon/exo-ruby-block-improvement

more details on arguments with default values
Merge branch 'master' of github.com:lewagon/promo-4-challenges
exo pmu & beautifulmycode