Podcast Chapter Proposal

Podcast Chapters are a feature supported by many [podcast clients](https://stratechery.com/outline/what-podcast-player-do-you-recommend/) already however the current standard is to [embed the chapter content into the MP3 file itself](https://id3.org/id3v2-chapters-1.0). This is podcast specific content and should be moved to the podcast RSS feed directly so it can be more easily accessed and updated by podcasters.

There is some precedent for moving this into the RSS Feed. The [Simple Chapters Specification](https://podlove.org/simple-chapters/) was introduced in 2012 and I've drawn on that spec heavily for this proposal for introduction in the Podcast Namespace.

README.md

@@ -116,6 +116,21 @@ this larger namespace.  But, we don't want to be so general that the spec become
    specified by the RSS \<language\> element.  If the rel="captions" attribute is present, the linked file is considered to be a closed captions file, regardless of what the
    mime type is.  In that scenario, time codes are assumed to be present in the file in some capacity.
 
+- **\<podcast:chapters/>**
+
+   Channel (optional | single)
+
+   This element lists optional `<podcast:chapter/>` item elements.
+
+- **\<podcast:chapter start="[(Normal Play Time)]" title="[(string)]" href="[(uri to content)]" type="[mime type]"/>**
+
+   Item (optional | multiple)
+
+   This element specifies a point in time during the podcast that can be linked to directly and optionally supplemented with additional content.
+   `start` is required and uses the [Normal Play Time](https://www.w3.org/TR/media-frags/#naming-time) standard.
+   `title` is required and is used as a user facing identifier for this chapter
+   `href` is optional and points to additional user facing content
+   `type` is optional but it is strongly encouraged if `href` is used so that clients can handle the chapter content appropriately
 
 - **\<podcast:alternateEnclosure type="[mime type]" length="[(int)]" bitrate="[(float)]" title="[(string)]" stream>**[uri of media asset]**\</podcast:alternateEnclosure>**