message: docs: add additional property to theme usage doc
diff: @@ -165,7 +165,7 @@ Also you can pass options:
  specUrl="http://rebilly.github.io/RebillyAPI/openapi.json"
  options={{
  nativeScrollbars: true,
  - theme: { colors: { main: '#dd5522' } },
  + theme: { colors: { primary { main: '#dd5522' } } },
  }}
  />
  ```
  