First round of USAGE docs.

Also, have the Result iterator auto-rewind when complete.

FossilOrigin-Name: d10c2e7dd8dd447cc33f1cfb6fbbd94946f56e8da912e1619673338d9c8a968d

tests/queries/t_auto_rewinds_the_iterator.nim

@@ -0,0 +1,16 @@
+# vim: set et sta sw=4 ts=4 :
+
+import kuzu
+
+let db = newKuzuDatabase()
+let conn = db.connect
+
+var q = conn.query """
+UNWIND [1,2,3] AS items
+RETURN items
+"""
+
+for row in q: discard
+
+assert q.hasNext == true
+