Fix rootFolder if --path is not defined (#360)

This way it will also find the docset.yml file if it's in the root

Author: reakaleek

src/Elastic.Markdown/BuildContext.cs

@@ -48,7 +48,7 @@ public BuildContext(IFileSystem readFileSystem, IFileSystem writeFileSystem, str
 
 		var rootFolder = !string.IsNullOrWhiteSpace(source)
 			? ReadFileSystem.DirectoryInfo.New(source)
-			: ReadFileSystem.DirectoryInfo.New(Path.Combine(Paths.Root.FullName, "docs"));
+			: ReadFileSystem.DirectoryInfo.New(Path.Combine(Paths.Root.FullName));
 		SourcePath = FindDocsFolderFromRoot(rootFolder);
 
 		OutputPath = !string.IsNullOrWhiteSpace(output)