message: docs: fix typo in form control readme
diff: @@ -6,7 +6,7 @@ form fields accessible by default.
  - **FormControl** - the top level component that provides context.
  - **FormLabel** - the visible form control label.
  -- **FormHelperText** - the from control's assistive text that guides the user.
  +- **FormHelperText** - the form control's assistive text that guides the user.
  If added, it hides when there's an error in the field.
  - **FormErrorMessage** - the form control's error feedback. If there's a help
  text visible when the control is invalid, it replaces the help text, to
  