feat(README): add dateAdded note

README.md

@@ -1,4 +1,4 @@
-Homebrew JSONs compatible with 5etools. An editor will be created eventually.
+Homebrew JSONs compatible with 5etools. An editor will be created Eventually:tm:.
 
 #### Getting brew (automatically)
 1. Hit the "Manage Homebrew" button (if available) on a 5etools page.
@@ -19,7 +19,7 @@ Homebrew JSONs compatible with 5etools. An editor will be created eventually.
 _**Note:** one large advantage of contributing to this repo, is that your files will be kept up-to-date as changes are made to the main site._
 
 - The easiest way to make your own is to copy one of the existing 'brews as a template and use the main [5etools data](https://github.com/TheGiddyLimit/TheGiddyLimit.github.io/tree/master/data) as a reference.
-- The schemata for the main site data can be found [here](https://github.com/TheGiddyLimit/TheGiddyLimit.github.io/tree/master/test/schema)
+    - The schemata for the main site data can be found [here](https://github.com/TheGiddyLimit/TheGiddyLimit.github.io/tree/master/test/schema)
 - Contributions are welcome. For the Git-literate, make a pull request. For everyone else, create an Issue and post a link to your file (PasteBin is fine), and I (or other maintainers, in future) can add it for you.
 
 A schema is available (`json.schema`) describing the layout of the and usage of the `_meta` property found in the various data files.
@@ -29,7 +29,8 @@ 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"
  - 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). 
+ - 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/).
 
 #### Useful links