The ping section needs to be added to the blueprint of the content that contains the links. E.g. if you are using a template article for blog posts, add the YML snippet to the blueprint blueprints/pages/article.yml - if you also have a template notes for notes, then similarly to blueprint notes.yml etc.
The meta information about sent pings will be stored in a JSON file within the same folder as the content (e.g. in case of an assumed template article: in the same folder where the markdown file article.txt is located).
Any of this is still subject to change in later versions, as I keep figuring out the best way to implement.