docs(templates): document the {{stream}} note template tag (#120, #121) (#196)

The {{stream}} tag was implemented in 208e783 (#120) but never documented.
Add it to the note-template tag list, noting that it resolves to the
episode's audio source URL and is exposed only in episode note templates
(not in file-path, download-path, transcript, or feed-note templates).

Ports the genuinely-missing documentation from #121. The tag itself is
already on master (208e783); that PR's `?? ""` guard is redundant
(episode.streamUrl is a required string, never null/undefined), and its
settings-placeholder edit would not compile (a trailing comma made the
added lines a second argument to setPlaceholder(), failing strict
typecheck with TS2554), so only the docs are carried over here.

Co-authored-by: João <monteiro.joao.ps@gmail.com>

Author: chhoumann

docs/docs/templates.md

@@ -29,6 +29,7 @@ This template will be used to create the note text. You can use the following sy
 
 - `{{podcast}}`: The name of the podcast.
 - `{{url}}`: The URL of the podcast episode.
+- `{{stream}}`: The direct URL of the episode's audio file — the RSS `<enclosure>` URL for podcast feeds, or the underlying audio source for Pocket Casts and local-file episodes. Handy for embedding the raw audio or linking to the source. An empty string is used in the rare case no audio URL is available. Available in episode note templates only.
 - `{{date}}`: The publish date of the podcast episode.
 	- You can use `{{date:format}}` to specify a custom [Moment.js](https://momentjs.com) format. E.g. `{{date:YYYY-MM-DD}}`.
 - `{{currentDate}}`: The current date — i.e. when the note is created — as opposed to `{{date}}`, which is the episode's publish date. Useful for a "captured on" metadata field.