feat(readme): add note about source uniqueness

README.md

@@ -28,6 +28,7 @@ A schema is available (`json.schema`) describing the layout of the and usage of
 
 There are a few conventions used which should be followed when creating homebrew:
  - Filename format is "Author Name; Homebrew Name.json"
+ - Use a unique `"json"` source name; they should be uniquely identifiable across all homebrew. For example, for the hypothetical book "A History Of Dragons" by "A. N. Other," a sensible source name would be `"ANOtherHistoryOfDragons"`. Note that this text is never displayed, so can be as long and as ugly as required. While this is not enforced, we reserve the right to change data as required to avoid naming conflicts.
  - Sources with no URL should use `https://github.com/TheGiddyLimit/homebrew` as the URL
  - Source `"author"` should only include content authors; conversion credit should be included in a `"convertedBy"` property (with the same format).
  - Metadata should include a `"dateAdded"` property, which is a Unix timestamp (in seconds) at which the file was added. See [here](https://github.com/TheGiddyLimit/homebrew/blob/master/spell/Sample%20-%20Giddy%3B%20Assorted%20Marginalia.json#L29) for an example of the structure; an example timestamp would be `1537874753`. You can view and copy the current Unix time [here](https://www.epochconverter.com/).