Small grammar fixes

Author: BNAndras

concepts/structs/introduction.md

@@ -1,6 +1,6 @@
 # Introduction
 
-C# `struct`s are closely related `class`s.
+C# `struct`s are closely related to `class`es.
 They have state and behavior.
 They have constructors that take arguments, instances can be assigned, tested for equality and stored in collections.