Minor, fix formatting in configuration doc.

src/docs/userguide/advanced_configuration.diviner

@@ -91,6 +91,7 @@ involved but may be easier in some deployment environments. Note that this needs
 to be set in your webserver environment, and also in your shell whenever you
 run a script:
 
+```
 # Shell
 export PHABRICATOR_ENV=custom/exampleconfig
 
@@ -104,6 +105,7 @@ run a script:
 setenv.add-environment = (
    "PHABRICATOR_ENV" => "custom/exampleconfig",
 )
+```
 
 After creating and selecting a configuration file, restart your webserver. Any
 configuration you set should take effect immediately, and your file should be