Add scabbard_storage key to example toml file
All keys should be documented/present in the example toml file. This
commit adds the key and some basic docs.
@@ -189,3 +189,6 @@ version = "1"
# Filter defines the level of log the logger writes to appenders.
# Valid filter options are, Trace, Debug, Info, Warn, and Error in decreasing order of verbosity.
#filter = "Warn"
+
+# Where scabbard will store its internal state, valid options are "database" or "lmdb"
+#scabbard_storage = "database"
