Update darwin platform support from amd64 to arm64 (#4461)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rkuris <3193068+rkuris@users.noreply.github.com>
Co-authored-by: Ron Kuris <swcafe@gmail.com>

Author: Copilot

README.md

@@ -224,11 +224,11 @@ AvalancheGo support tiers:
 | :----------: | :--------------: | :-----------: |
 |    amd64     |      Linux       |       1       |
 |    arm64     |      Linux       |       2       |
-|    amd64     |      Darwin      |       2       |
+|    arm64     |      Darwin      |       2       |
+|    amd64     |      Darwin      | Not supported |
 |    amd64     |     Windows      | Not supported |
 |     arm      |      Linux       | Not supported |
 |     i386     |      Linux       | Not supported |
-|    arm64     |      Darwin      | Not supported |
 
 To officially support a new platform, one must satisfy the following requirements: