docs(plugins): note that plugins should be applied before you call `m…

…ongoose.model()`

Fix #7723

docs/plugins.pug

@@ -27,6 +27,7 @@ block content
     <ul class="toc">
       <li><a href="#example">Example</a></li>
       <li><a href="#global">Global Plugins</a></li>
+      <li><a href="#apply-plugins-before-compiling-models">Apply Plugins Before Compiling Models</a></li>
       <li><a href="#official">Officially Supported Plugins</a></li>
     </ul>
 
@@ -84,6 +85,39 @@ block content
     const Player = mongoose.model('Player', playerSchema);
     ```
 
+    <h3 id="apply-plugins-before-compiling-models"><a href="#apply-plugins-before-compiling-models">Apply Plugins Before Compiling Models</a></h3>
+
+    Because many plugins rely on [middleware](/docs/middleware.html), you should make sure to apply plugins **before**
+    you call `mongoose.model()` or `conn.model()`. Otherwise, [any middleware the plugin registers won't get applied](/docs/middleware.html#defining).
+
+    ```javascript
+    // loadedAt.js
+    module.exports = function loadedAtPlugin(schema, options) {
+      schema.virtual('loadedAt').
+        get(function() { return this._loadedAt; }).
+        set(function(v) { this._loadedAt = v; });
+
+      schema.post(['find', 'findOne'], function(docs) {
+        if (!Array.isArray(docs)) {
+          docs = [docs];
+        }
+        const now = new Date();
+        for (const doc of docs) {
+          doc.loadedAt = now;
+        }
+      });
+    };
+
+    // game-schema.js
+    const loadedAtPlugin = require('./loadedAt');
+    const gameSchema = new Schema({ ... });
+    const Game = mongoose.model('Game', gameSchema);
+
+    // `find()` and `findOne()` hooks from `loadedAtPlugin()` won't get applied
+    // because `mongoose.model()` was already called!
+    gameSchema.plugin(loadedAtPlugin);
+    ```
+
     <h3 id="official"><a href="#official">Officially Supported Plugins</a></h3>
 
     The Mongoose team maintains several plugins that add cool new features to