move four_banger to bpiphany (#16082)

keyboards/four_banger/readme.md → keyboards/bpiphany/four_banger/readme.md

@@ -9,6 +9,6 @@ Hardware Availability: [1up Keyboards](https://1upkeyboards.com/)
 
 Make example for this keyboard (after setting up your build environment):
 
-    make four_banger:default
+    make bpiphany/four_banger: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.
+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.