Correct grammar in instructions.append.md (#623)

* Correct grammar in instructions.append.md

* Correct grammar in instructions.append.md

* Update exercises/practice/grade-school/.docs/instructions.append.md

Co-authored-by: Erik Schierboom <erik_schierboom@hotmail.com>

---------

Co-authored-by: Erik Schierboom <erik_schierboom@hotmail.com>

exercises/practice/grade-school/.docs/instructions.append.md

@@ -1,3 +1,7 @@
 # Instructions append
 
-It isn't strictly necessary to model students as a seperate object, you can use a convenient internal data strcture as the requirements are quite simple (and as long as it doesn't leak out into the results).Note: this exercise has been slightly modified from the problem-specification, as it makes more sense to seperate adding students and querying them in seperate methods (vs. having one method doing both, which feels less Pharo/Smalltalk like).
+It isn't strictly necessary to model students as a separate object, you can use a convenient internal data structure as the requirements are quite simple (and as long as it doesn't leak out into the results).
+
+~~~~exercism/note
+This exercise has been slightly modified from the problem-specification, as it makes more sense to separate adding students and querying them in separate methods (vs. having one method doing both, which feels less Pharo/Smalltalk like).
+~~~~