docs: Update upgrade guide

UPGRADE.md

@@ -8,7 +8,9 @@ before finalizing the upgrade process.
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+
 - [master](#master)
+- [v0.17.0-beta.1+oryOS.12](#v0170-beta1oryos12)
 - [v0.16.0-beta.1+oryOS.12](#v0160-beta1oryos12)
   - [Access Rule Changes](#access-rule-changes)
   - [Mutators (formerly credentials issuers)](#mutators-formerly-credentials-issuers)
@@ -37,6 +39,11 @@ before finalizing the upgrade process.
 
 ## master
 
+## v0.17.0-beta.1+oryOS.12
+
+ORY Oathkeeper now watches configuration files and access rules repositories on the local disk for changes. This does currently
+not work for remote sources (http/https). Additionally, access rules can now be written in YAML (expected file extensions are `yaml` and `yml`).
+
 ## v0.16.0-beta.1+oryOS.12
 
 ORY Oathkeeper was changed according to discussion