TOC update to align with title update. (SharePoint#750)

* Edit pass.

* A few more edits.

* Fix TOC title to match updated topic title.

Author: Lauragra

misc/SharePointDocumentationToc.xml

@@ -31,7 +31,7 @@
 				<Item text="Build ListView Command Set" url="spfx/extensions/get-started/building-simple-cmdset-with-dialog-api" SEODescription="Build a ListView Command Set, which uses dialog API." />
 			</Item>
 			<Item text="Guidance" url="spfx/extensions/get-started">
-				<Item text="Using custom dialogs" url="spfx/extensions/guidance/using-custom-dialogs-with-spfx" SEODescription="Using Custom Dialogs with SharePoint Framework Extensions." />
+				<Item text="Use custom dialog boxes" url="spfx/extensions/guidance/using-custom-dialogs-with-spfx" SEODescription="Using Custom Dialogs with SharePoint Framework Extensions." />
 			</Item>
 		</Item>
 		<Item text="Web parts" url="spfx/web-parts" SEODescription="">