indicate reference files

packages/flirt/src/App.jsx

@@ -14,6 +14,7 @@ import {
 } from 'widgets'
 import Button from '@mui/material/Button';
 import Checkbox from '@mui/material/Checkbox';
+import Typography from '@mui/material/Typography';
 import FormControlLabel from '@mui/material/FormControlLabel';
 
 export default function App() {
@@ -192,7 +193,8 @@ export default function App() {
 
       {/* reference file chooser */}
       <FileChooser value={opts['-ref']} textLabel="Reference" onClick={onRefFileClick}/>
-      <Row gap={2} width={'100%'}>
+      <Row gap={2} width={'100%'} alignItems='center'>
+        <Typography variant="body" fontFamily={'sans-serif'}>Choose reference:</Typography>
         <Button onClick={onMNI1mmClick}>MNI 1mm brain</Button>
         <Button onClick={onMNI2mmClick}>MNI 2mm brain</Button>
       </Row>