Add "Explore ADaM templates" article

[manciniedoardo]

In line with the main admiral package's update, please could you add a page to your website to explore the ADaM templates that your extension package provides:

You can see the {admiral} version of this vignette here, and this is the source file that you can copy and use. You'll also need to add here as a suggested package in the DESCRIPTION. Please nest this new article under "Get Started":

The article also creates IDs for subsection, so you can link to them from other vignettes:

ADaM | Sample Code
---- | --------------
[`ADXX`](templates.html#adxx) | `admiral::use_ad_template("ADXX", package = "admiraltemplate")`

Note: It's important that we make this an article and not a vignette because we don't want to ship it with the package.

[manciniedoardo]

@ukey1025 want to try this?