doc: test: suggest multi-line imports in functional test style guide

test/functional/example_test.py

@@ -14,8 +14,15 @@ is testing and *how* it's being tested
 from collections import defaultdict
 
 # Avoid wildcard * imports
-from test_framework.blocktools import (create_block, create_coinbase)
-from test_framework.messages import CInv, MSG_BLOCK
+# Use lexicographically sorted multi-line imports
+from test_framework.blocktools import (
+    create_block,
+    create_coinbase,
+)
+from test_framework.messages import (
+    CInv,
+    MSG_BLOCK,
+)
 from test_framework.p2p import (
     P2PInterface,
     msg_block,