add full path to doc

Co-authored-by: Marco Pracucci <[email protected]>

Author: bboreham

docs/guides/security.md

@@ -7,7 +7,6 @@ slug: security
 
 Cortex must be deployed with due care over system configuration, using principles such as "least privilege" to limit any exposure due to flaws in the source code.
 
-You must configure authorisation and authentication externally to Cortex; see [this guide](auth)
+You must configure authorisation and authentication externally to Cortex; see [this guide](./authentication-and-authorisation.md)
 
 Information about security disclosures and mailing lists is [in the main repo](https://github.com/cortexproject/cortex/blob/master/SECURITY.md)
-