Improve grade-school description

exercises/grade-school/description.md

@@ -1,21 +1,21 @@
 # Description
 
-Given students' names along with the grade that they are in, create a roster for the school.
+Given students' names along with the grade they are in, create a roster for the school.
 
 In the end, you should be able to:
 
-- Add a student's name to the roster for a grade
+- Add a student's name to the roster for a grade:
   - "Add Jim to grade 2."
   - "OK."
-- Get a list of all students enrolled in a grade
+- Get a list of all students enrolled in a grade:
   - "Which students are in grade 2?"
-  - "We've only got Jim just now."
+  - "We've only got Jim right now."
 - Get a sorted list of all students in all grades.
-  Grades should sort as 1, 2, 3, etc., and students within a grade should be sorted alphabetically by name.
-  - "Who all is enrolled in school right now?"
+  Grades should be sorted as 1, 2, 3, etc., and students within a grade should be sorted alphabetically by name.
+  - "Who is enrolled in school right now?"
   - "Let me think.
-    We have Anna, Barb, and Charlie in grade 1, Alex, Peter, and Zoe in grade 2 and Jim in grade 5.
-    So the answer is: Anna, Barb, Charlie, Alex, Peter, Zoe and Jim"
+    We have Anna, Barb, and Charlie in grade 1, Alex, Peter, and Zoe in grade 2, and Jim in grade 5.
+    So the answer is: Anna, Barb, Charlie, Alex, Peter, Zoe, and Jim."
 
-Note that all our students only have one name (It's a small town, what do you want?) and each student cannot be added more than once to a grade or the roster.
-In fact, when a test attempts to add the same student more than once, your implementation should indicate that this is incorrect.
+Note that all our students only have one name (it’s a small town, what do you want?), and each student cannot be added more than once to a grade or the roster.
+If a test attempts to add the same student more than once, your implementation should indicate that this is incorrect.