Note the need for async mode

Author: DavidSpickett

lldb/test/API/commands/register/register/register_command/TestRegisters.py

@@ -665,6 +665,7 @@ def test_process_must_be_stopped(self):
         self.build()
         exe = self.getBuildArtifact("a.out")
         pid = self.spawnSubprocess(exe, ["wait_for_attach"]).pid
+        # Async so we can enter commands while the process is running.
         self.setAsync(True)
         self.runCmd("process attach --continue -p %d" % pid)