Fix frame-ancestors docs from none to self to not break Jitsi (#21128)

README.md

@@ -104,7 +104,7 @@ If you are using nginx, this would look something like the following:
 add_header X-Frame-Options SAMEORIGIN;
 add_header X-Content-Type-Options nosniff;
 add_header X-XSS-Protection "1; mode=block";
-add_header Content-Security-Policy "frame-ancestors 'none'";
+add_header Content-Security-Policy "frame-ancestors 'self'";
 ```
 
 For Apache, the configuration looks like:

docs/kubernetes.md

@@ -162,7 +162,7 @@ Then you can deploy it to your cluster with something like `kubectl apply -f my-
           add_header X-Frame-Options SAMEORIGIN;
           add_header X-Content-Type-Options nosniff;
           add_header X-XSS-Protection "1; mode=block";
-          add_header Content-Security-Policy "frame-ancestors 'none'";
+          add_header Content-Security-Policy "frame-ancestors 'self'";
     spec:
       rules:
         - host: element.example.nl