Update README.md

Author: ziteh

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 *PR Micro* is a Pro Micro compatible RP2040 board with USB Type-C, inspired by the [plut0nium/0xB2](https://github.com/plut0nium/0xB2) and [joshajohnson/sea-picro](https://github.com/joshajohnson/sea-picro).
 
+[Demo video](https://youtu.be/CSA7Ih7nAls)
+
 Go to [Releases](https://github.com/ziteh/rp-micro/releases) for Gerber, schematic and PCBA files.
 
 > A part of [ErgoSNM keyboard](https://github.com/ziteh/ergo-snm-keyboard) project.