explain vim stack trace usage

README

@@ -48,6 +48,7 @@ Then you'll have to register the exception listener, for example (in your config
     services:
         vim.stack_trace:
             class: VimExceptionHandler
+            arguments: [ 'dev-vim-server' ] # optional vim server name, defaults to 'dev'
             tags:
                 -  { name: 'kernel.event_listener', event: 'kernel.exception', method: 'onKernelException' }
 
@@ -57,3 +58,8 @@ To use it in another system, just use the same class by typing:
     VimExceptionHandler::register();
 
 
+Then launch vim using:
+
+    vim --servername dev-vim-server
+
+