docs(testing): note that tmachine runs on macOS

TESTING.md

@@ -232,14 +232,14 @@ nix run .#openshell-test-runner -- \
   --family conformance --package conformance
 ```
 
-It needs KVM, and tmachine only boots guests of the host's architecture. The
-runner points the tests at the installed CLI and the gateway the installer
-registered (`--gateway`, default `openshell`). A run passes if nextest
-succeeds; nextest fails a run with no tests. The runner exits with 1 when a
-test failed and 2 when the run could not complete, for example because the
-environment didn't come up. It writes `junit.xml`, `nextest.log` and, after a
-failure, the guest's diagnostics to `artifacts/test-results/` (`--results`),
-even when the run timed out.
+It needs KVM on Linux or the Hypervisor framework on macOS, and tmachine only
+boots guests of the host's architecture. The runner points the tests at the
+installed CLI and the gateway the installer registered (`--gateway`, default
+`openshell`). A run passes if nextest succeeds; nextest fails a run with no
+tests. The runner exits with 1 when a test failed and 2 when the run could not
+complete, for example because the environment didn't come up. It writes
+`junit.xml`, `nextest.log` and, after a failure, the guest's diagnostics to
+`artifacts/test-results/` (`--results`), even when the run timed out.
 
 `--filter <filterset>` narrows the tests with a nextest filterset, and
 `--keep` leaves the VM running until you press Enter. Two runs on one host