LFKeyboards Mini1800: refactor into revisions (#16260)

* fork Mini1800 into reva and revc versions

* update info.json

- apply friendly formatting
- update maintainer value

* update keymap rules.mk formatting

- align inline comments
- convert tabs to spaces

* align keymap rules.mk files to QMK template

* move common keymap rules.mk settings to revision level

* info.json: correct key sequence

* align revision rules.mk files to QMK template

* clean up revision rules.mk files

* add readme files for each revision

* correct USB Product string

* remove post_rules.mk files

The internal settings were commented out, so the files actually don't do anything.

* edit Bootloader instructions on main readme

* move non-assignment rules to post_rules.mk

* add inline comments for NKRO_ENABLE per fauxpark

keyboards/lfkeyboards/mini1800/reva/readme.md

@@ -0,0 +1,22 @@
+# Mini1800 RevA
+
+* Keyboard Maintainer: [LFKeyboards](https://github.com/lfkeyboards)
+* Hardware Supported: Mini1800 RevA (Green PCB with AT90USB1286)
+* Hardware Availability: [LFKeyboards.com](https://www.lfkeyboards.com/)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make lfkeyboards/mini1800/reva:default
+
+Flashing example for this keyboard:
+
+    make lfkeyboards/mini1800/reva:default:flash
+
+## Bootloader
+
+To reset the board into bootloader mode, do one of the following:
+
+* **Physical reset button**: Briefly press the button on the bottom of the PCB (between Q and W keys)
+* **Keycode in keymap**: Press the key mapped to `RESET` if it is available (`Fn`+`Right Shift`, then tap `Enter` by 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).