Improve style in tim-from-marketing/.docs/introduction.md (#2319)

Nothing major, just a few small adjustments I thought improved it slightly.

Author: NateEag

exercises/concept/tim-from-marketing/.docs/introduction.md

@@ -4,7 +4,7 @@
 
 In C#, the `null` literal is used to denote the absence of a value. A _nullable_ type is a type that allows for `null` values.
 
-Prior to C# 8.0, reference types were always nullable and value types were not. A value type can be made nullable though by appending it with a question mark (`?`).
+Prior to C# 8.0, reference types were always nullable and value types were not. A value type can be made nullable by appending a question mark to it (`?`).
 
 ```csharp
 string nullableReferenceType = "hello";
@@ -17,7 +17,7 @@ int? nullableValueType = 5; // Define nullable value type
 nullableValueType = null;   // Valid as type is nullable
 ```
 
-Accessing a member of a variable which value is `null` will compile fine, but result in a `NullReferenceException` being thrown at runtime:
+Accessing a null variable's member does not cause a compile error, but results in a `NullReferenceException` being thrown at runtime:
 
 ```csharp
 string sentence = null;
@@ -36,7 +36,7 @@ string? nullableReferenceType = "movie";
 nullableReferenceType = null; // Valid as type is nullable
 ```
 
-To safely work with nullable values, one should check if they are `null` before working with them:
+To safely work with nullable values, check if they are `null` before using them:
 
 ```csharp
 string NormalizedName(string? name)
@@ -45,12 +45,10 @@ string NormalizedName(string? name)
     {
         return "UNKNOWN";
     }
-    else
-    {
-        // Value is not null at this point, so no compile warning
-        // and no runtime NullReferenceException being thrown
-        return name.ToUpper();
-    }
+
+    // Value is not null at this point, so no compile warning
+    // and no runtime NullReferenceException being thrown
+    return name.ToUpper();
 }
 
 NormalizedName(null); // => "UNKNOWN"