fix missing bits from help strings

Author: svlandeg

docs/tutorial/arguments/optional.md

@@ -135,7 +135,7 @@ $ python main.py --help
 Usage: main.py [OPTIONS] [name]
 
 Arguments:
-  [name]
+  [name]  [default: World]
 
 Options:
   --help                Show this message and exit.

docs/tutorial/typer-app.md

@@ -66,6 +66,9 @@ $ python main.py  --help
 
 Usage: main.py [OPTIONS] {name}
 
+Arguments:
+  name  [required]
+
 Options:
   --install-completion  Install completion for the current shell.
   --show-completion     Show completion for the current shell, to copy it or customize the installation.