amp-nested-submenu docs show import script

[sebastianbenz]

amp-nested-submenu does not need to be explicitly imported (which will result in validation error). We need to handle the case in the overview table generator when the extension script does not need to be imported. It probably also makes sense to mention this in the docs.

//cc @CrystalOnScript for thoughts

[CrystalOnScript]

Is it possible to add frontmatter to component docs for required-script: true/false and replace the area in the table with "No Script Required read below for further details" or something when it doesn't? This case is tricky, since it does require amp-sidebar. Maybe replace the required script with that?

[patrickkettner]

@CrystalOnScript is this still valid?