reword playground definition as suggested

Co-authored-by: Eric Hellman <[email protected]>

Author: davorpa

Diff for: docs/CONTRIBUTING.md

@@ -23,7 +23,7 @@ By contributing you agree to respect the [Code of Conduct](CODE_OF_CONDUCT.md) o
     - *Books* : PDF, HTML, ePub, a gitbook.io based site, a Git repo, etc.
     - *Courses* : A course is a learning material which is not a book. [This is a course](http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-006-introduction-to-algorithms-fall-2011/).
     - *Interactive Tutorials* : An interactive website which lets the user type code or commands and evaluates the result (by "evaluate" we don't mean "grade"). e.g.: [Try Haskell](http://tryhaskell.org), [Try GitHub](http://try.github.io).
-    - *Playgrounds* : are online and interactive websites, games or desktop software useful to learn playing. Therefore, you can write, compile (or run), and share this code snippets with others. They also usually allows you to fork and get your hands dirty by playing around with other's code.
+    - *Playgrounds* : are online and interactive websites, games or desktop software for learning programming. Write, compile (or run), and share code snippets. Playgrounds often allow you to fork and get your hands dirty by playing with code.
     - *Podcasts and Screencasts* : Podcasts and screencasts.
     - *Problem Sets & Competitive Programming* : A website or software which lets you assess your programming skills by solving simple or complex problems, with or without code review, with or without comparing the results with other users.