arcvm: Add a debugging tip to the VM adapter

BUG=None
TEST=try, no real code change

Change-Id: Ib552103883e98a83e7748a47c5a755f34b34b708
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2018003Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734979}

components/arc/session/arc_vm_client_adapter.cc

@@ -177,6 +177,15 @@ vm_tools::concierge::StartArcVmRequest CreateStartArcVmRequest(
     request.add_params("rw");
   }
   request.add_params("init=/init");
+
+  // TIP: When you want to see all dmesg logs from the Android system processes
+  // such as init, uncomment the following line. By default, the guest kernel
+  // rate-limits the logging and you might not be able to see all LOGs from
+  // them. The logs could be silently dropped. This is useful when modifying
+  // init.bertha.rc, for example.
+  //
+  // request.add_params("printk.devkmsg=on");
+
   for (auto& entry : kernel_cmdline)
     request.add_params(std::move(entry));