Describe prometheus in daml-on-sql README (#10307)

* Describe prometheus in daml-on-sql README
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* changes post-review

ledger/daml-on-sql/README.rst

@@ -382,6 +382,11 @@ command-line interface options:
     value ``2003`` will be used. A ``metric_prefix`` can be specified, causing
     all metrics to be reported with the specified prefix.
 
+  - ``prometheus://<server_host>[:<server_port>]``: renders captured metrics
+    on an HTTP endpoint in accordance with the prometheus protocol. If the port
+    is omitted, the default value ``55001`` will be used. The metrics will be
+    available under the address ``http://<server_host>:<server_port>/metrics``.
+
 - ``--metrics-reporting-interval``: metrics are pre-aggregated within the *Daml
   for PostgreSQL* server and sent to the reporter, this option allows the user
   to set the interval. The formats accepted are based on the ISO-8601 duration
@@ -506,8 +511,8 @@ A meter. Number of deduplicated commands.
 A meter. Number of delayed submissions (submission who have been evaluated to
 transaction with a ledger time farther in the future than the expected latency).
 
-``daml.commands.failed_command_interpretation``
------------------------------------------------
+``daml.commands.failed_command_interpretations``
+------------------------------------------------
 
 A meter. Number of commands that have been deemed unacceptable by the
 interpreter and thus rejected (e.g. double spends)