README.md: Add SoundID Reference to Cask list

README.md

@@ -77,6 +77,7 @@ Casks included in this Tap:
 - [`bpm`][bpm] - A lightweight beats-per-minute tapper for the Mac status bar.
 - [`ndi-tools`][ndi-tools] -  NDI® Tools a free suite of applications and tools
   for NDI VoIP streaming.
+- [`soundid-reference`][soundid-reference] - Calibration software for headphones and speakers.
 
 ### Upgrading
 
@@ -181,3 +182,4 @@ Copyright (C) © 🄯  2022-2023 James Cuzella
 [1]: https://docs.brew.sh/Cask-Cookbook#stanza-installer
 [bpm]: https://github.com/bencmbrook/bpm
 [ndi-tools]: https://www.ndi.tv/tools/
+[soundid-reference]: https://www.sonarworks.com/soundid-reference