improve flag desc

cmd/beacon-chain/sync/backfill/flags/flags.go

@@ -21,7 +21,7 @@ var (
 		Name: backfillBatchSizeName,
 		Usage: "Number of blocks per backfill batch. " +
 			"A larger number will request more blocks at once from peers, but also consume more system memory to " +
-			"hold batches in memory during processing. This has a multiplicative effect with " + backfillWorkerCountName,
+			"hold batches in memory during processing. This has a multiplicative effect with " + backfillWorkerCountName + ".",
 		Value: 64,
 	}
 	// BackfillWorkerCount allows users to tune the number of concurrent backfill batches to download, to maximize
@@ -30,9 +30,9 @@ var (
 		Name: backfillWorkerCountName,
 		Usage: "Number of concurrent backfill batch requests. " +
 			"A larger number will better utilize network resources, up to a system-dependent limit, but will also " +
-			"consume more system memory to hold batches in memory during processing. Multiply by backfill-batch-size and " +
+			"consume more system memory to hold batches in memory during processing. Multiply by " + backfillBatchSizeName + " and " +
 			"average block size (~2MB before deneb) to find the right number for your system. " +
-			"This has a multiplicative effect with " + backfillBatchSizeName,
+			"This has a multiplicative effect with " + backfillBatchSizeName + ".",
 		Value: 2,
 	}
 )