Update supervisor_001_draft.md (#333)

* Update supervisor_001_draft.md

If the only node in the *FullNodes* set is the primary, that was just deemed faulty, we can't find honest primary.

* Update supervisor_001_draft.md

spec/light-client/supervisor/supervisor_001_draft.md

@@ -208,7 +208,7 @@ initialization. Initially this set is partitioned into
 
 - one full node that is the *primary* (singleton set),
 - a set *Secondaries* (of fixed size, e.g., 3),
-- a set *FullNodes*.
+- a set *FullNodes*; it excludes *primary* and *Secondaries* nodes.
 - A set *FaultyNodes* of nodes that the light client suspects of
     being faulty; it is initially empty