Updated missing file mess

MarkdownSource/notfound.md

@@ -0,0 +1,6 @@
+Not found (404) page
+====================
+
+`Docnet` will automatically create a not found (404) page in the root of the destination folder named `404.htm`.
+
+If no `404.md` file is found in the root of the source folder, the file will be generated with default content. If a file is found, the `404.md` will be used to generate the not found (404) page.