document the new CLI command

docs/usage/stored_procedures.md

@@ -14,9 +14,23 @@ In this guide, we'll look at how to use stored procedures with the ndc-sqlserver
 
 ## Tracking Stored Procedures
 
-The ndc-sqlserver connector can track stored procedures in a SQL Server database. The stored
-procedures present in the database are automatically added while introspecting the database
-via the `update` operation. The stored procedures will appear in the `$.metadata.storedProcedures`
+The ndc-sqlserver connector can track stored procedures in a SQL Server database.
+
+The stored procedures present in the database can be added by running the following command:
+
+```
+ddn connector plugin --connector app/sqlserver/connector.yaml -- stored-procedures
+```
+
+If you want to overwrite the existing stored procedures,
+
+```
+ddn connector plugin --connector app/sqlserver/connector.yaml -- stored-procedures --overwrite
+```
+
+
+
+After running the above command, the stored procedures will appear in the `$.metadata.storedProcedures`
 key of the configuration that is generated by the `update` operation.
 
 
@@ -99,6 +113,12 @@ we can add a return type for it, as following:
 }
 ```
 
+### Marking required arguments as `nonNullable`
+
+If your stored procedure contains a required argument, then you can mark the argument as `nonNullable`
+which will enable to throw a validation error as soon as possible. For example, in the above, the `Phone` field
+is a required argument, hence it is marked as `nonNullable`.
+
 ## Schema of Stored Procedures
 
 ## Schema