DOC fix and clean up documentation links

Fixed relative paths in features section
Removed link to non-existent markdown file

docs/en/userguide/index.md

@@ -24,7 +24,7 @@ Here are a few tips to get you started:
 - Ensure you have the necessary consents for processing and storing data according to your legislation (e.g. GDPR)
 - Only accept form submissions via encrypted transfers (HTTPS) - check our [Secure Coding](https://docs.silverstripe.org/en/developer_guides/security/secure_coding/) guidelines
 - Control access to form submissions (via CMS page access controls)
-- Control access to files uploaded with submissions (via [folder access controls](field-types.md#file-upload-field))
+- Control access to files uploaded with submissions (via [folder access controls](02_field-types.md#file-upload-field))
 - Create a process to limit the types of data you are allowed to collect via this feature (e.g. no payment information or health data)
 - Create a process for limiting submission storage duration (manual deletion)
 - Consider further safeguards such as at-rest encryption (check [encryption related addons](https://addons.silverstripe.org/add-ons?search=encrypt))