[Keymap] Add pierrec83's gherkin keymap (#9465)

* [Keymap] Add pierrec83's gherkin keymap

Contribute my gherkin keymap upstream as it is semi-stable. It has grown
in symbiosis with my Kyria keymap which is already upstream.

Add a readme

* Remove generated keymap and instructions to generate it as it is done by qmk flash

keyboards/40percentclub/gherkin/keymaps/pierrec83/config.h

@@ -0,0 +1,31 @@
+#pragma once
+
+/* Make layout the right way:
+ *  - USB port on left side
+ *  - Switches facing the correct way
+ */
+#undef MATRIX_ROW_PINS
+#undef MATRIX_COL_PINS
+#define MATRIX_ROW_PINS { B6, B2, B3, B1, F7 }
+#define MATRIX_COL_PINS { D0, D4, C6, D7, E6, B4 }
+
+// Set the mouse settings to a comfortable speed/accuracy trade-off
+// Assume the screen refresh rate is 60 Htz or higher
+// The default is 50. This makes the mouse ~3 times faster and more accurate
+#define MOUSEKEY_INTERVAL 16
+// The default is 20. Since we made the mouse about 3 times faster with the previous setting,
+// give it more time to accelerate to max speed to retain precise control over short distances.
+#define MOUSEKEY_TIME_TO_MAX 40
+// The default is 300. Let's try and make this as low as possible while keeping the cursor responsive
+#define MOUSEKEY_DELAY 100
+// It makes sense to use the same delay for the mouseweel
+#define MOUSEKEY_WHEEL_DELAY 100
+// The default is 100
+#define MOUSEKEY_WHEEL_INTERVAL 50
+// The default is 40
+#define MOUSEKEY_WHEEL_TIME_TO_MAX 100
+
+#define TAPPING_TERM 200
+#define PERMISSIVE_HOLD
+#define IGNORE_MOD_TAP_INTERRUPT
+#define TAPPING_FORCE_HOLD

keyboards/40percentclub/gherkin/keymaps/pierrec83/readme.md

@@ -0,0 +1,38 @@
+@pierrec83's keymap for the gherkin
+===
+
+A usable keymap for the gherkin's 30 keys layout, somewhat in sync with my Kyria keymap.
+
+This keymap is more or less an adaptation of my Kyria keymap which sacrifices some convenience but retains most functionality.
+
+Features
+---
+* Mouse keys with constants tuned so the keyboard usable for me as my sole pointing device
+* Homerow layers activation
+* Minimal side-index motion thanks to workman base layer and similar principles in other layers
+* Two symbol layers, both activated with one homerow key and either another key on the same hand's homerow or a key from the other hand
+* Mousing around, including left and right clicking can be done either one-handed or fully on the homerow with both hands
+* Easy chaining of common command line or vim patterns, such as `~/`, `()`, `ESC : w ENTER` etc.
+* Common OS shortcuts like switching workspaces on gnome or MacOS easily accessible (for the shortcuts I use. This may not apply to others)
+
+Instructions to update the keymap
+---
+
+For now, I am still more comfortable updating the keymap through the qmk configurator as I don't trust myself to manually keep comments describing the keymap in sync with the code itself. This means that my keymap.c is generated and not really readable. For a readble view of my keymap, one must import keymap.json into [qmk configurator](https://config.qmk.fm) and use the web UI or print it.
+
+To update the keymap,
+* Load keymap.json into qmk configurator
+* Perform any edits
+* Export the keymap. This should save a json file in `~/Downloads/pierrec83.json` or equivalent for your OS
+* From the root of qmk_firmware, move the keymap to its destination:
+```
+mv ~/Downloads/pierrec83.json keyboards/40percentclub/gherkin/keymaps/pierrec83/keymap.json
+```
+* Flash the firmware (for instance, if left hand is plugged):
+```
+qmk flash -kb 40percentclub/gherkin -km pierrec83
+```
+
+Author
+---
+I am @pierrec83 on Twitter, @pierrechevalier83 on github. I chose the shorter nickname for my keymap.

keyboards/40percentclub/gherkin/keymaps/pierrec83/rules.mk

@@ -0,0 +1 @@
+BACKLIGHT_ENABLE = yes