correctly refer to "using directives"

Address incorrect use of ["using statement"](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-statement) to refer to a ["using directive"](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-directive).

Author: mrlacey

docs/extensibility/walkthrough-using-a-shell-command-with-an-editor-extension.md

@@ -93,7 +93,7 @@ From a VSPackage, you can add features such as menu commands to the editor. This
 
     9. WindowsBase
 
-3. Add the following `using` statement.
+3. Add the following `using` directive.
 
     ```csharp
     using Microsoft.VisualStudio.Text;
@@ -129,7 +129,7 @@ From a VSPackage, you can add features such as menu commands to the editor. This
 
 1. Create a class in the CommentAdornmentTest project, and name it `CommentBlock`.
 
-2. Add the following `using` statements.
+2. Add the following `using` directives.
 
     ```csharp
     using Microsoft.VisualStudio.Text;
@@ -253,7 +253,7 @@ From a VSPackage, you can add features such as menu commands to the editor. This
 
 1. Add a class file to the CommentAdornmentTest project and name it `Connector`.
 
-2. Add the following `using` statements.
+2. Add the following `using` directives.
 
     ```csharp
     using System.ComponentModel.Composition;
@@ -317,7 +317,7 @@ From a VSPackage, you can add features such as menu commands to the editor. This
 
 1. Add a new class file to the CommentAdornmentTest project and name it `CommentAdornmentProvider`.
 
-2. Add the following `using` statements.
+2. Add the following `using` directives.
 
     ```csharp
     using System;
@@ -481,7 +481,7 @@ From a VSPackage, you can add features such as menu commands to the editor. This
 
 1. Add a class file to the CommentAdornmentTest project and name it `CommentAdornmentManager`.
 
-2. Add the following `using` statements.
+2. Add the following `using` directives.
 
     ```csharp
     using System;
@@ -606,7 +606,7 @@ From a VSPackage, you can add features such as menu commands to the editor. This
 
     - Microsoft.VisualStudio.Text.UI.Wpf
 
-2. Open the *AddAdornment.cs* file and add the following `using` statements.
+2. Open the *AddAdornment.cs* file and add the following `using` directives.
 
     ```csharp
     using Microsoft.VisualStudio.TextManager.Interop;