re-structure project, add readme

.gitignore

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+web-ext-artifacts

README.md

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+# open-with
+
+A simple WebExtension to play back media in an external player.
+
+## Compatibilty
+
+*open-with* was originally intended to use [mpv] via the [youtube-dl] hook for a long list of [supported sites]. However, it will also work with other media players with [M3U] support, e.g. VLC, for direct media URLs.
+
+## About
+
+There have been addons on [AMO] prior to the release of *open-with*, but they depend on [native-messaging]. This WebExtension is designed to work on its own, without the need to install native messaging software on the host.
+
+This is achieved by creating a plain text file with the M3U header, paste the current link into it and open the downloaded M3U playlist in your preferred media player.
+
+![Screenshot](screenshot.png)
+
+## Credits
+
+This project is licensed under the [GPL]. The used [icon] is from Mozilla's [Photon] collection and licensed under the [MPL].
+
+<!-- References -->
+[AMO]: https://addons.mozilla.org/
+[GPL]: COPYING
+[icon]: src/icons/play-16.svg
+[m3u]: https://en.wikipedia.org/wiki/M3U
+[MPL]: https://www.mozilla.org/en-US/MPL/2.0/
+[mpv]: https://mpv.io/
+[native-messaging]: https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Native_messaging
+[Photon]: https://design.firefox.com/icons/viewer/#play
+[supported sites]: https://rg3.github.io/youtube-dl/supportedsites.html
+[youtube-dl]: https://youtube-dl.org/
+

manifest.json → src/manifest.json

@@ -1,5 +1,5 @@
 {
-  "description": "Open current URL in external application.",
+  "description": "Play media on current URL in external application.",
   "manifest_version": 2,
   "name": "open-with",
   "version": "1.0",