[Keyboard] add kb2040 flavor of gherkin (qmk#18360)

keyboards/40percentclub/gherkin/kb2040/readme.md

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+# Gherkin
+
+![Gherkin](https://i.imgur.com/XrqqtTq.jpg)
+![KB2040](https://cdn-shop.adafruit.com/640x480/5302-12.jpg)
+
+===
+
+A 30 key keyboard with Adafruit's KB2040 as microcontroller.
+
+* [The original TMK firmware](https://github.com/di0ib/tmk_keyboard/tree/master/keyboard/gherkin)
+
+Keyboard Maintainer: QMK Community 
+Hardware Supported: Gherkin PCB & Adafruit KB2040
+Hardware Availability: [Gherkin project on 40% Keyboards](https://www.40percent.club/2016/11/gherkin.html) and [Adafruit KB2040](https://www.adafruit.com/product/5302)
+
+Make example for this keyboard (after setting up your build environment):
+
+ make 40percentclub/gherkin/kb2040:default
+
+See the [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) and the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information. Brand new to QMK? Start with our [Complete Newbs Guide](https://docs.qmk.fm/#/newbs).
+
+Use the KB2040 microcontroller as a drop-in replacement for the Pro Micro in this cute 30% keyboard.

keyboards/40percentclub/gherkin/kb2040/rules.mk

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+CONVERT_TO = kb2040

keyboards/40percentclub/gherkin/readme.md

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 # Gherkin
 
-![Gherkin](https://4.bp.blogspot.com/-sQ18-lNZXOc/WCzlTde-4PI/AAAAAAAB_JQ/qQrehAMG6DMKf3i4oj4mkmLGOfTUvb3KgCLcB/s640/IMG_20161116_122926.jpg)
+![Gherkin](https://i.imgur.com/XrqqtTq.jpg)
 ===
 
 A 30 key keyboard.