add hyperlinks for sql commands

Signed-off-by: Richard Chien <stdrc@outlook.com>

processing/sql/transactions.mdx

@@ -8,7 +8,7 @@ Transactions in databases refer to logical units of work that consist of one or
 
 RisingWave supports read-only transactions, where all reads within a transaction are executed against the consistent Hummock snapshot. Hummock is the LSM-Tree-based storage engine in RisingWave that is specifically optimized for streaming workloads.
 
-To initiate a transaction, use either the `START TRANSACTION READ ONLY` or `BEGIN READ ONLY` command. Subsequently, you can execute queries to read data from the consistent snapshot. To finalize the transaction and submit the queries as a single unit, use the `COMMIT` command.
+To initiate a transaction, use either the [`START TRANSACTION READ ONLY`](/sql/commands/sql-start-transaction) or [`BEGIN READ ONLY`](/sql/commands/sql-begin) command. Subsequently, you can execute queries to read data from the consistent snapshot. To finalize the transaction and submit the queries as a single unit, use the [`COMMIT`](/sql/commands/sql-commit) command.
 
 Please note that data modifications are not allowed while a transaction is initiated but not yet committed. The statements listed below are not allowed within a transaction: