XD75RE Custom layout, and clarification in readme.md (#1754)

XD75RE Custom layout, and clarification in readme.md (#1754)

* Duplicate default layout as basis of my own

* Basic Colemak layer, just to practice flashing

* Add reset button so that we don't have to short out the reset button on the board to flash it.

* Symbols layer

* Navigation layer, and remove unused keys. Now usable, nice.

* Correct backspace for UK QWERTY mapping

* Small clarification in XD75RE readme instructions

* Use UK pipe so that I can type a pipe on a UK keyboard