[Keyboard] Io mini1800 (#16115)

* First commit

* first commit

* 2x3u layout functional

* 625u layout

* rotary encoder

* Modifications to keymaps

* Remove ingrained from io_mini branch

* Update readme

* Update info.json

* change hardware availability

* Change rules.mk wording to match other PR

* Update keyboards/io_mini1800/rules.mk

* Update keyboards/io_mini1800/keymaps/default/keymap.c

* Update keyboards/io_mini1800/keymaps/2x3u/keymap.c

* Update keyboards/io_mini1800/io_mini1800.c

* Update keyboards/io_mini1800/keymaps/2x3u/readme.md

* Update keyboards/io_mini1800/readme.md

keyboards/io_mini1800/readme.md

@@ -0,0 +1,24 @@
+# io_mini1800
+
+This keyboard is a mini 1800 with a minimal navigation cluster, which also offers a rotary encoder option.
+
+* Keyboard Maintainer: [s8erdude](https://github.com/jpuerto96)
+* Hardware Supported: IO-Mini 1800
+* Hardware Availability: [P3D Store](https://p3dstore.com/)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make io_mini1800:default
+
+Flashing example for this keyboard:
+
+    make io_mini1800:default:flash
+
+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).
+
+## Bootloader
+
+To reset the board into bootloader, do one of the following:
+
+* **Hardware reset**: short the pad labeled RESET on the back, near the microcontroller
+* **Bootmagic reset**: hold down the top left key (usually programmed as Escape) while plugging in the keyboard (also resets persistent storage)