Initial structure for Ergodox as subprojects

Only the EZ default keymaps compiles at the moment though.

keyboards/ergodox/keymaps/twey/readme.md

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+# Twey's Home Configuration
+## Layers
+- Layer 0: Non-ANSI Dvorak layout, with modified modifiers — all
+  modifiers on thumb keys, as well as return and space.
+- Layer 1: Default symbol layout.
+- Layer 2: Plover-oriented stenography layer.
+- Layer 3: Extended media/mouse layout.
+
+## Unusual features
+The Plover key (top right key on the left half) also sends my Plover
+‘toggle’ chord (SH-FT) when pressed, as well as toggling the steno
+layer, so you can toggle between steno and typing modes with a single
+keypress.
+
+If you want to use this feature, you'll need to add the
+`commands.json` dictionary to your Plover dictionaries, or define the
+toggle stroke (`PHROLG`) yourself.