Make File > Open more self-explanatory

Summary:
Yesterday I saw someone try to open the xcode executable with the File > Open function.

This made me realise it's not clear what this is for, and you might think it can open all kinds of things.

Reviewed By: danielbuechele

Differential Revision: D17225496

fbshipit-source-id: 893360a1f450a8db25be34fce6c288e8db8f9626

src/utils/exportData.tsx

@@ -521,6 +521,9 @@ export function showOpenDialog(store: Store) {
   remote.dialog.showOpenDialog(
     {
       properties: ['openFile'],
+      filters: [
+        {extensions: ['flipper', 'json', 'txt'], name: 'Flipper files'},
+      ],
     },
     (files: Array<string>) => {
       if (files !== undefined && files.length > 0) {