Update Levinson readme to support elite-c (#4445)

* init - updated levinson readme to support elite-c

* updated readme per PR comment

* added trailing spaces to lines 6 7 8

* updated readme bootloader instructions

* updated readme

* updated readme

keyboards/levinson/readme.md

@@ -4,17 +4,25 @@ Levinson
 A split 40% split 4x12 ortholinear keyboard made and sold by Keebio. It's essentially a Let's Split with LED backlight support and 2u thumb key support. [More info at Keebio](https://keeb.io).
 
 Keyboard Maintainer: [Bakingpy/nooges](https://github.com/nooges)  
-Hardware Supported: Pro Micro  
+Hardware Supported: Pro Micro, Elite-C  
 Hardware Availability: [Keebio](https://keeb.io)  
 
 Make example for this keyboard (after setting up your build environment):
 
     make levinson/rev2:default
 
-Example of flashing this keyboard:
+Example of flashing this keyboard with Pro micro:
 
     make levinson/rev2:default:avrdude
 
-See [build environment setup](https://docs.qmk.fm/build_environment_setup.html) then the [make instructions](https://docs.qmk.fm/make_instructions.html) for more information.
+Example of flashing this keyboard with Elite-C:
+
+You'll need to add `BOOTLOADER = atmel-dfu` to your `rules.mk` to ensure that resetting the board works properly.
+
+Hold the reset button on the Elite-C board, or the reset button on the keyboard if already assembled, then release the button and run:
+
+    make levinson/rev2:default:dfu
+
+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).
 
 A build guide for this keyboard can be found here: [Levinson Build Guide](https://docs.keeb.io)