Add upgrade notes for 1.13

content/docs/installation/upgrading/upgrading-1.12-1.13.md

@@ -0,0 +1,19 @@
+---
+title: Upgrading from v1.12 to v1.13
+description: 'cert-manager installation: Upgrading v1.12 to v1.13'
+---
+
+When upgrading cert-manager from 1.12 to 1.13, in few cases you might need to take additional steps to ensure a smooth upgrade:
+
+1. BREAKING: If you deploy cert-manager using helm and have `.featureGates` value set, the features defined
+there will no longer be passed to cert-manager webhook, only to cert-manager controller. Use `webhook.featureGates` field
+instead to define features to be enabled on webhook. (https://github.com/cert-manager/cert-manager/pull/6093, https://github.com/irbekrm)
+
+2. Potentially breaking: If you were, for some reason, passing cert-manager controller's features to webhook's --feature-gates flag,
+this will now break (unless the webhook actually has a feature by that name). (https://github.com/cert-manager/cert-manager/pull/6093, https://github.com/irbekrm)
+
+3. Potentially breaking: Webhook validation of CertificateRequest resources is stricter now: all `KeyUsages` and `ExtendedKeyUsages` must be defined directly in the CertificateRequest resource, the encoded CSR can never contain more usages that defined there. (https://github.com/cert-manager/cert-manager/pull/6182, https://github.com/inteon)
+
+## Next Steps
+
+From here on you can follow the [regular upgrade process](./README.md).