docs: generalize reasoning for deferred initialization

Co-authored-by: William Bergamin <wbergamin@salesforce.com>

Author: zimeg

slack_bolt/middleware/request_verification/request_verification.py

@@ -26,8 +26,7 @@ def __init__(self, signing_secret: str, base_logger: Optional[Logger] = None):
 
     @property
     def verifier(self) -> SignatureVerifier:
-        # Defer initialization to avoid errors of a missing signing secret for
-        # apps using Socket Mode connections
+        # Defer initialization to avoid errors during start up
         if self._verifier is None:
             self._verifier = SignatureVerifier(signing_secret=self._signing_secret)
         return self._verifier