Add zrt to TLS 1.3 API options (#20400)

See SPM-2727 for more info.

Author: Duncan-Cloudflare

src/content/docs/ssl/edge-certificates/additional-options/tls-13.mdx

@@ -35,7 +35,7 @@ To enable TLS 1.3 in the dashboard:
 
 </TabItem> <TabItem label="API">
 
-To adjust your TLS 1.3 settings with the API, send a [`PATCH`](/api/resources/zones/subresources/settings/methods/edit/) request with `tls_1_3` as the setting name in the URI path, and set the `value` parameter to your desired setting (`"on"` or `"off"`).
+To adjust your TLS 1.3 settings with the API, send a [`PATCH`](/api/resources/zones/subresources/settings/methods/edit/) request with `tls_1_3` as the setting name in the URI path, and set the `value` parameter to your desired setting (`"on"`, `"zrt"` or `"off"`). `zrt` refers to [Zero Round Trip Time Resumption (0-RTT)](https://blog.cloudflare.com/introducing-0-rtt/).
 
 </TabItem> </Tabs>