Fix typo in buildAndProgram.md.

Add documentation about companion apps + link to videos.

doc/CompanionApps/Amazfish.md

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+#Amazfish
+[Amazfish](https://openrepos.net/content/piggz/amazfish) is a companion app that supports many smartwatches and activity trackers running on [SailfishOS](https://sailfishos.org/).
+
+## Features
+The following features are implemented:
+ - Scanning & detection of Pinetime-JF / InfiniTime
+ - Connection / disconnection
+ - Time synchronization
+ - Notifications
+ - Music control
+ 
+## Demo
+[This video](https://seafile.codingfield.com/f/21c5d023452740279e36/) shows how to connect to the Pinetime and control the playback of the music on the phone.
+Amazfish and Sailfish OS are running on the [Pinephone](https://www.pine64.org/pinephone/), another awesome device from Pine64.
+ 

doc/CompanionApps/Gadgetbridge.md

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+# Integration with Gadgetbridge
+[Gadgetbridge](https://gadgetbridge.org/) is an Android application that supports many smartwatches and fitness trackers.
+
+The integration of InfiniTime (previously Pinetime-JF) is ongoing in a [feature branch](https://codeberg.org/Freeyourgadget/Gadgetbridge/src/branch/pinetime-jf).
+
+## Features
+The following features are implemented:
+ - Scanning & detection of Pinetime-JF / InfiniTime
+ - Connection / disconnection
+ - Notifications
+ 
+## Demo
+[This video](https://seafile.codingfield.com/f/0a2920b9d765462385e4/) shows how to scan, connect, send notification (using the debug screen) and disconnect from the Pinetime.

doc/CompanionApps/NrfconnectOTA.md

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+# OTA using NRFConnect
+[NRFConnect](https://www.nordicsemi.com/Software-and-tools/Development-Tools/nRF-Connect-for-mobile) is a powerful application (running on Android and iOS) which allows to scan and connect to BLE devices.
+
+## Features
+ - Scanning, connect, disconnect
+ - Time synchronization
+ - OTA
+ 
+InfiniTime implements the Nordic DFU protocol for the OTA functionality. NRFConnect also supports this protocol.
+
+# Demo
+[This video](https://seafile.codingfield.com/f/a52b69683a05472a90c7/) shows how to use NRFConnect to update the firmware running on the Pinetime.