Add Go vanity import example
add eleventy example

This patch adds an Eleventy (https://www.11ty.dev/) sample manifest.

Due to the nature of Node.js development, this example is somewhat more
opinionated than the Hugo example:

* A version of Node.js must be specified, so I chose the current LTS
* The environment variable `CI` is necessary to avoid flooding the
  console with a fancy progress bar during `npm install`.
* This example assumes the repository already contains a `package.json`
  file with `@11ty/eleventy` in its dependencies.

I've also tweaked the style in the following ways:

* De-mystify some of the workings of this manifest by linking to
  documentation where appropriate.
Add Zola example
Initial commit