Compilation fixes for handwired/concertina/64key (#11987)

* concatenate config.h to 64key directory

* move rules.mk to 64key directory

This commit makes the firmware actually compile.

* insert complete rules.mk contents

Conforms the file to QMK's template.

* move info.json to 64key directory

* remove concertina.h

This file no longer serves a purpose now that everything is in the 64key directory.

* complete 64key readme.md

Conforms the file more to QMK's template.

keyboards/handwired/concertina/64key/readme.md

@@ -1,5 +1,8 @@
-The `64key` layout
-==================
+# Concertina 64-key
+
+![Concertina 64-key](https://raw.githubusercontent.com/noroadsleft/qmk_images/master/keyboards/handwired/concertina/64key/concertina-1-side-view.jpg)
+
+A diploid, concave, columnar keyboard.
 
 This folder represents the keyboard configuration identified as
 `concertina_64key` in the DMOTE application’s list of GNU make targets, as of
@@ -13,3 +16,17 @@ not run Colemak.
 
 A full set of printable caps to match the keymap is available in the
 `dmote-keycap` application, [here](https://github.com/veikman/dmote-keycap).
+
+* Keyboard Maintainer: [Viktor Eikman](https://github.com/veikman)
+* Hardware Supported: Concertina 64-key case, Pro Micro (ATmega32U4)
+* Hardware Availability: [viktor.eikman.se](https://viktor.eikman.se/article/the-concertina/)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make handwired/concertina/64key:default
+
+Flashing example for this keyboard:
+
+    make handwired/concertina/64key: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).