Given a project with no default items, and a readme.md alongside the project, the readme will be set as the package readme in metadata, but the item will not be included in the package, since it isn't present already as a None item (which we use for the inference).

We should apply the same heuristics we use to populate the metadata value (i.e. the file exists) to always include it, even if it's not in None or Content already.