NIU Mini Settings update and Refactor (#6651)

* update codebase to four-space indent

* update codebase to use #pragma once

* refactor config.h

* change info.json to debug linting

* refactor readme

- file header
- update docs links

* minimize and lint rules.mk

* change features

- enable mousekeys and nkro

* use GPIO commands for Status LED

Co-Authored-By: fauxpark <fauxpark@gmail.com>

* use IS_LED_ON macro

Co-Authored-By: fauxpark <fauxpark@gmail.com>

* update compile/flash examples in readme

* :flash doesn't use QMK Toolbox

keyboards/niu_mini/readme.md

@@ -1,5 +1,4 @@
-NIU Mini
-===
+# NIU Mini
 
 ![NIU Mini](https://cdn.shopify.com/s/files/1/1473/3902/files/40__01.jpg)
 
@@ -11,6 +10,10 @@ Hardware Availability: [KBDFans](https://kbdfans.myshopify.com/products/niu-mini
 
 Make example for this keyboard (after setting up your build environment):
 
-    make niu_mini:default:dfu
+    make niu_mini:default
 
-See [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) then the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information.
+Flashing example for this keyboard ([using the command line](https://docs.qmk.fm/#/newbs_flashing?id=flash-your-keyboard-from-the-command-line)):
+
+    make niu_mini: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).