Update middlewar.pug file

the documentation does not specificly addresses that both properties 'query' and 'document' must be assigned in order for the 'remove' middleware to execute for the right context (that is on the query or the document).

docs/middleware.pug

@@ -329,17 +329,17 @@ block content
     You can pass options to [`Schema.pre()`](/docs/api.html#schema_Schema-pre)
     and [`Schema.post()`](/docs/api.html#schema_Schema-post) to switch whether
     Mongoose calls your `remove()` hook for [`Document.remove()`](/docs/api.html#model_Model-remove)
-    or [`Model.remove()`](/docs/api.html#model_Model.remove):
+    or [`Model.remove()`](/docs/api.html#model_Model.remove). Note here that you need to set both `document` and `query` properties in the passed object:
 
     ```javascript
     // Only document middleware
-    schema.pre('remove', { document: true }, function() {
+    schema.pre('remove', { document: true, query: false}, function() {
       console.log('Removing doc!');
     });
 
     // Only query middleware. This will get called when you do `Model.remove()`
     // but not `doc.remove()`.
-    schema.pre('remove', { query: true }, function() {
+    schema.pre('remove', { query: true, document: flse }, function() {
       console.log('Removing!');
     });
     ```