Add download link for nightly macOS arm build (#286)

* add download link for nightly macOS arm build
* update macos nightly downloads URL

Author: capital-G

_data/downloads.yml

@@ -40,8 +40,10 @@ os:
         name: Bleeding Edge
         end_text: This is the latest build of the development branch.
         downloads:
-          - name: Latest build
-            link: http://supercollider.s3.amazonaws.com/builds/supercollider/supercollider/osx/develop-latest.html
+          - name: Latest x64 build
+            link: http://supercollider.s3.amazonaws.com/builds/supercollider/supercollider/macos-x64/develop-latest.html
+          - name: Latest arm build
+            link: http://supercollider.s3.amazonaws.com/builds/supercollider/supercollider/macos-arm64/develop-latest.html
 
   - name: Linux
     slug: Linux