custom_vm.md: Add instructions for serial console

Bug: 335362012
Test: eyeball
Change-Id: I564406578a60455a7ef98fe96b2562de0b8ae885
diff --git a/docs/custom_vm.md b/docs/custom_vm.md
index 39223e8..1e15d16 100644
--- a/docs/custom_vm.md
+++ b/docs/custom_vm.md
@@ -289,6 +289,8 @@
 
 ```
 $ adb shell pm clear com.android.virtualization.vmlauncher
+# or
+$ adb shell pm clear com.google.android.virtualization.vmlauncher
 ```
 
 ### Inside guest OS (for ChromiumOS only)
@@ -305,11 +307,20 @@
 
 ### Debugging
 
-To see console log, check
+To open the serial console (interactive terminal):
+```shell
+$ adb shell -t /apex/com.android.virt/bin/vm console
+```
+
+To see console logs only, check
 `/data/data/com.android.virtualization.vmlauncher/files/console.log`
 Or
 `/data/data/com.google.android.virtualization.vmlauncher/files/console.log`
 
+```shell
+$ adb shell su root tail +0 -F /data/data/com{,.google}.android.virtualization.vmlauncher/files/console.log
+```
+
 For ChromiumOS, you can ssh-in. Use following commands after network setup.
 
 ```shell