update generate outputs command reference (#8258)

Author: ykethan

src/pages/[platform]/reference/cli-commands/index.mdx

@@ -231,7 +231,15 @@ npx ampx generate outputs --stack amplify-nextamplifygen2-josef-sandbox-ca85e108
 Similar to `sandbox`, you can specify an alternate outputs file format by using `--format`:
 
 ```bash title="Terminal" showLineNumbers={false}
-npx ampx generate outputs --stack amplify-nextamplifygen2-josef-sandbox-ca85e1081b
+npx ampx generate outputs --stack amplify-nextamplifygen2-josef-sandbox-ca85e1081b --format dart
+```
+
+#### Use with pre-existing branch
+
+If you have a pre-existing branch that you want to generate outputs for, you can use the `--branch` with the `--app-id` flag:
+
+```bash title="Terminal" showLineNumbers={false}
+npx ampx generate outputs --branch staging --app-id <your-amplify-app-id>
 ```
 
 ## npx ampx generate graphql-client-code
@@ -266,7 +274,7 @@ Optional parameters:
 #### Generate GraphQL client code using the Amplify App ID and branch. 
 
 ```bash title="Terminal" showLineNumbers={false}
-npx ampx generate graphql-client-code --app-id <your-amplify-app-id>	--branch staging
+npx ampx generate graphql-client-code --app-id <your-amplify-app-id> --branch staging
 ```
 
 #### Generate GraphQL client code for a branch that is connected to Amplify