[varnish] fix default.vcl path

varnish/content.md

@@ -23,7 +23,7 @@ backend default {
 Then run:
 
 ```console
-$ docker run --name my-running-varnish -v /path/to/default.vcl:/usr/local/etc/varnish/default.vcl:ro --tmpfs /usr/local/var/varnish:exec -d %%IMAGE%%
+$ docker run --name my-running-varnish -v /path/to/default.vcl:/etc/varnish/default.vcl:ro --tmpfs /usr/local/var/varnish:exec -d %%IMAGE%%
 ```
 
 Alternatively, a simple `Dockerfile` can be used to generate a new image that includes the necessary `default.vcl` (which is a much cleaner solution than the bind mount above):