[Keymap] Add custom Planck Light keymap (#5464)

* Create custom Planck Light keycap

See README for details

* Link to WhatPulse in README

* More remapping, and add RGB LED effects

* Remove dead code, address PR feedback from drashna

keyboards/planck/keymaps/tom/readme.md

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+# tomholford's layout
+
+This layout is data-driven: I installed [WhatPulse](https://whatpulse.org/) a few months ago and generated a heatmap of the most frequently used keys. I also optimized for my most-used programming languages, and muscle memory.
+
+## Changes from Default
+
+### QWERTY
+
+- swap escape and tab
+- rearrange arrows in original layout
+- swap rshift and Enter
+- map / to original location of left arrow key
+
+### RAISE
+
+- move backslash to backspace
+- map quote to original location from qwerty layer
+- map brightness up / down to original location of left and up arrows
+- map volume up / down to original location of down and right arrows
+
+### LOWER
+
+- move pipe to backspace
+- map quote to original location from qwerty layer
+- map brightness up / down to original location of left and up arrows
+- map volume up / down to original location of down and right arrows
+
+
+## RGB LED
+
+- Illuminate when pressing RAISE, LOWER, or ADJUST ([source](https://www.reddit.com/r/olkb/comments/8wvk8s/custom_rgb_configuration_by_keycodelayer/))