Add Service token to conf in single vm documentation

This is probably the 3rd time i got bitten by this, So
filing a review :)

Change-Id: Icd0834dda9c7ef806eb0fe976de85130e0220781
diff --git a/doc/source/guides/single-machine.rst b/doc/source/guides/single-machine.rst
index 17e9b9e..70287a9 100644
--- a/doc/source/guides/single-machine.rst
+++ b/doc/source/guides/single-machine.rst
@@ -108,6 +108,7 @@
     MYSQL_PASSWORD=iheartdatabases
     RABBIT_PASSWORD=flopsymopsy
     SERVICE_PASSWORD=iheartksl
+    SERVICE_TOKEN=xyzpdqlazydog
 
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