[Keymap] Add yhaliaw keymap for Planck/Rev6.1. (#11318)

keyboards/planck/keymaps/yhaliaw/readme.md

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+# yhaliaw Planck layout
+
+The layout for Planck by yhaliaw. 
+
+Developed and tested on Planck Rev 6.1.
+
+## Features
+
+Leader sequences can be used to turn on layers without holding the key and reset the layers.
+Leader sequences are triggered by key the series of key in quick succession.
+See Base layer notes in Layout section.
+
+Successful leader sequences will play the planck sound if sound is enabled.
+
+The RGB underglow is linked to the layers and capslock.
+
+## Keycodes
+
+Most Keycodes are standard [QMK keycodes](https://docs.qmk.fm/#/keycodes).
+
+### Custom Keycodes
+
+The `RESET` key to start the bootloader is access by a leader sequence.
+This is done to prevent a mispress.
+See Adjust layer notes in Layout section.
+
+The `Clear` key is used to clear the EEPROM of the keyboard.
+This can be seen as resetting the state of the keyboard. 
+Replug the keyboard to load in the resetted states.
+
+## Layout
+![yhaliaw planck layout](https://i.imgur.com/HvYva64.png)