Massive update for all boards

boards/boardsource/3x4/README.md

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+# Boardsource 3x4
+
+![Boardsource3x4](https://boardsource.imgix.net/30171267-d988-46cc-ba03-9f6a8ab96487.jpg?raw=true)
+
+This macro pad / small 12 key was inspired by the plaid look
+
+kb.py is designed to work with the nice!nano
+
+Retailers (USA)  
+[Boardsource](https://boardsource.xyz/store/5ecc2008eee64242946c98c1)  
+
+Extentions enabled by default  
+- [Layers](https://github.com/KMKfw/kmk_firmware/tree/master/docs/layers.md) Need more keys than switches? Use layers.