[docs] Brush up the documentation

* Try to organize after expected user need
* Update mkdocs stuff and fix a broken link
* Move web building info to building.md
* Add info about Roku Soundbridge
* Add note about Google Nest not working

docs/audio-outputs/mobile.md

@@ -0,0 +1,19 @@
+# Listening on your Mobile Device
+
+## iOS
+
+On iOS, the options are limited because there are no Media Client apps with DAAP
+support and because Apple doesn't allow AirPlay receiver apps. OwnTone also
+can't share music via Home Sharing, which is the protocol Apple uses for sharing
+media between devices.
+
+That leaves the following options, which all rely on OwnTone's streaming:
+
+- listen via the [web interface](web.md)
+- use a [MPD client app](../control-clients/mobile.md#mpd-client-apps) that supports local playback
+- connect to the [streaming](streaming.md) endpoint with a media player like VLC
+
+## Android
+
+On Android, you can use the same streaming methods described for iOS, but you
+can also find apps that act as AirPlay receivers.