Add a comment for peer channel fetch

Signed-off-by: YoungHypo <haiboyang@smail.nju.edu.cn>

src/api-engine/api/lib/peer/channel.py

@@ -127,6 +127,8 @@ def fetch(self, block_path, channel, orderer_general_url, max_retries=5, retry_i
             ]
 
         LOG.info(" ".join(command))
+
+        # Retry fetching the block up to max_retries times
         for attempt in range(1, max_retries+1):
             try:
                 LOG.debug("Attempt %d/%d to fetch block", attempt, max_retries)