clarify default CompletionItem-behaviour

src/vs/vscode.d.ts

@@ -2017,6 +2017,12 @@ declare namespace vscode {
 	 * A completion item represents a text snippet that is
 	 * proposed to complete text that is being typed.
 	 *
+	 * It is suffient to create a completion item from just
+	 * a [label](#CompletionItem.label). In that case the completion
+	 * item will replace the [word](#TextDocument.getWordRangeAtPosition)
+	 * until the cursor with the given label.
+	 *
+	 *
 	 * @see [CompletionItemProvider.provideCompletionItems](#CompletionItemProvider.provideCompletionItems)
 	 * @see [CompletionItemProvider.resolveCompletionItem](#CompletionItemProvider.resolveCompletionItem)
 	 */