Readme for passed_failed function

Author: polishExperiment

workshop_registration_infakt_cracow/ex1/README.md

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+### Group students into passed and failed.
+
+---
+
+Write a function that returns hash of failed and passed students.
+
+**Requirements:**
+* function takes 2 arguments:
+  * first argument is a hash of students and their grades
+  * second argument is a threshold that divides students between
+those who passed and those who failed
+* function returns hash with two keys - `:failed` and `:passed`, each containing
+hash with failed and passed students
+* function should work flawlessly even when second argument is a string
+
+**Example usage:**  
+```ruby
+hash = {"Mark" => 10, "Ellen" => 65, "Roger" => 20, "Mike" => 70}
+passed_or_failed(hash, "65")
+```
+
+__Output__:  
+```ruby
+=> { passed: { "Ellen" => 65, "Mike" => 70 }, failed: { "Mark" => 10, "Roger" => 20 } }
+```