[Keymap] Adding bdk keymap for ergobox_ez (#4850)

* Adding bdk keymap

* Updating keymap after review from drashna

keyboards/ergodox_ez/keymaps/bdk/readme.md

@@ -0,0 +1,36 @@
+# The BDK Ergodox Keyboard Layout
+
+## Dvorak-based
+
+This was the first alternative layout I switched to and I don't want to change
+again.
+
+## Mod-tap / Layer-tap is great for thumb keys
+
+This means a key that activates a layer/modifier when you hold it down, but
+results in a keyclick when you tap it.  Thumb keys are great for this since
+they are good for both high-usage keys as well as modifiers.
+
+The one thing to avoid is when you mean to tap a key, but hit the next key
+before you release, which results in the modifier/layer instead of a tap.  To
+avoid this, I chose Enter/Tab as the tap keys, since they aren't chorded
+together with other keys often.
+
+The other issue is I found several problems with using the standard MT,LT code,
+so I rolled my own to handle it.
+
+## Don't have too many layers
+
+My first layouts had multiple layers that I could switch to, but that
+overloaded my brain.  This layout basically only uses 1 extra layer.
+Technically there's also a function key layer, but I only use those keys for
+a handlful of things: boot order, rename, reload page, that's basically it.
+
+## Brackets should be easy to use
+
+There's a lot of ways to lay out a symbol layer.  I organized mine around
+making the {[()]} chars easy to use since they're so frequent in programming.
+I put them all on the symbol layer home row.
+
+I also arranged the numbers so 0/1 were also on the symbol layer home row.
+This makes for fairly easy chording of "[0]" and "[1]".