Rename RST de-asserted label to 'RST de-asserted — ATR follows'

- More precise than 'ATR STARTS' (the ATR starts after the de-assert
  delay, not at the edge) while staying human-friendly; reads as a pair
  with 'RESET ASSERTED'
- Update tests and both READMEs (backend-only, no version bump)

tests/test_decode.py

@@ -2405,7 +2405,7 @@ class TestLineEvents(unittest.TestCase):
     def test_rst_deasserted(self):
         r = self._dec('rst', '000100')
         self.assertEqual(r['event'], 'reset de-asserted')
-        self.assertEqual(r['label'], 'ATR STARTS')
+        self.assertEqual(r['label'], 'RST de-asserted — ATR follows')
         self.assertEqual(r['level'], 'high')
 
     def test_vcc_on(self):
@@ -2431,7 +2431,7 @@ class TestLineEvents(unittest.TestCase):
             db.insert_message(sid, 0.1, 'rst', bytes.fromhex('000100'), 0)
             db.insert_message(sid, 0.2, 'vcc', bytes.fromhex('010100'), 0)
             msgs = db.get_messages(sid)
-            self.assertEqual(msgs[0]['decoded']['label'], 'ATR STARTS')
+            self.assertEqual(msgs[0]['decoded']['label'], 'RST de-asserted — ATR follows')
             self.assertEqual(msgs[1]['decoded']['label'], 'VCC ON (power-up)')
 
     def test_sniff_routing(self):