Fill in the upgrading documentation

Signed-off-by: Richard Wall <[email protected]>

Author: wallrj

content/docs/releases/upgrading/upgrading-1.15-1.16.md

@@ -5,7 +5,12 @@ description: 'cert-manager installation: Upgrading v1.15 to v1.16'
 
 Before upgrading cert-manager from 1.15 to 1.16 please read the following important notes about breaking changes in 1.16:
 
-TODO
+1. Helm schema validation may reject your existing Helm values files if they contain typos or unrecognized fields.
+   For more details, refer to the [Helm](../release-notes/release-notes-1.16.md#helm) section in the release notes.
+1. Venafi Issuer may fail to renew certificates if the requested duration conflicts with the CA’s minimum or maximum policy settings in Venafi.
+   For more details, refer to the [Venafi Issuer](../release-notes/release-notes-1.16.md#venafi-issuer) section in the release notes.
+1. Venafi Issuer may fail to renew Certificates if the issuer has been configured for TPP with username-password authentication.
+   For more details, refer to the [Venafi Issuer](../release-notes/release-notes-1.16.md#venafi-issuer) section in the release notes.
 
 ## Next Steps