Massdrop keyboards readme update (#3791)

Massdrop keyboards readme update for flashing instructions

keyboards/massdrop/alt67/readme.md

@@ -12,4 +12,9 @@ Make example for this keyboard (after setting up your build environment):
 
     make alt67:default
 
+For information on flashing this keyboard, visit the following links:
+
+[Massdrop Loader Releases](https://github.com/Massdrop/mdloader/releases/tag/0.0.1)  
+[Massdrop Loader Repository and Instructions](https://github.com/Massdrop/mdloader)
+
 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).

keyboards/massdrop/ctrl/readme.md

@@ -12,4 +12,9 @@ Make example for this keyboard (after setting up your build environment):
 
     make ctrl:default
 
+For information on flashing this keyboard, visit the following links:
+
+[Massdrop Loader Releases](https://github.com/Massdrop/mdloader/releases/tag/0.0.1)  
+[Massdrop Loader Repository and Instructions](https://github.com/Massdrop/mdloader)
+
 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).