feat: spf13#1140 updating doc gen docs for new method

site/content/docgen/md.md

@@ -79,6 +79,12 @@ func GenMarkdownTreeCustom(cmd *Command, dir string, filePrepender, linkHandler
 }
 ```
 
+```go
+func GenMarkdownTreeCustomWithFooter(cmd *Command, dir string, filePrepender, fileAppender, linkHandler func(string) string) error {
+	//...
+}
+```
+
 ```go
 func GenMarkdownCustom(cmd *Command, out *bytes.Buffer, linkHandler func(string) string) error {
 	//...
@@ -105,6 +111,8 @@ filePrepender := func(filename string) string {
 }
 ```
 
+The `fileAppender` will append the return value given the full filepath to the rendered Markdown file.
+
 The `linkHandler` can be used to customize the rendered internal links to the commands, given a filename:
 
 ```go