Fix typo in README for upload fields error

Author: NovaDev404

README.md

@@ -38,5 +38,5 @@ ProSign app source URL: https://prostore-ios.github.io/apps.json
 - [x] Replace status text with a progress bar on the Signing page.
 - [x] Add expiry dates to certificates.
 - [ ] Fix indenting visual bug on certificates page.
-- [ ] Resolve missing file errors in upload fields.
+- [ ] Resolve occasional missing file errors in upload fields.
 - [ ] Include an option to add official certificates when adding new certs.