docs: Add header hint for generate-schema to "Workflows" page (#322)

Co-authored-by: Phil Pluckthun <phil@kitten.sh>

website/get-started/workflows.md

@@ -36,6 +36,15 @@ gql.tada generate schema 'http://api.test/graphql' --output './schema.graphql'
 When no `--output` argument is passed, the command will attempt to
 use your configuration's `schema` setting, provided it's a file path.
 
+You may also pass `--header` arguments, which define headers sent
+during the GraphQL introspection request. If a GraphQL endpoint
+requires authentication headers, you may use this to pass in
+tokens or authorization headers.
+
+```sh
+gql.tada generate schema 'http://api.test/graphql' --header "Authorization: $ENV_TOKEN"
+```
+
 <a href="/reference/gql-tada-cli#generate-schema" class="button">
   <h4>CLI Reference</h4>
   <p>Learn more about the <code>generate-schema</code> command</p>