add linux_arm64 to package_index.template

Author: umbynos

package_index.template

@@ -16,6 +16,13 @@
               "size": "%%SIZE_LINUX_ARM%%",
               "checksum": "SHA-256:%%SHA_LINUX_ARM%%"
             },
+            {
+              "host": "aarch64-linux-gnu",
+              "url": "http://downloads.arduino.cc/tools/%%FILENAME_LINUX_ARM64%%",
+              "archiveFileName": "%%FILENAME_LINUX_ARM64%%",
+              "size": "%%SIZE_LINUX_ARM64%%",
+              "checksum": "SHA-256:%%SHA_LINUX_ARM64%%"
+            },
             {
               "host": "x86_64-linux-gnu",
               "url": "http://downloads.arduino.cc/tools/%%FILENAME_LINUX_AMD64%%",