Adding a warning note on the single-instance plugin instructing to keep the plugin init() call as the first one.

Author: charlesschaefer

src/content/docs/plugin/single-instance.mdx

@@ -70,6 +70,13 @@ Install the Single Instance plugin to get started.
 
 </Tabs>
 
+
+:::warning
+
+The Single Instance plugin must be the first one to be init()'ed to work well. Doing so prevents other plugins to initiate and eventually interfering with the app's instance that is already running.
+
+:::
+
 ## Usage
 
 The plugin is already installed and initialized, and it should be functioning correctly right away. Nevertheless, we can also enhance its functionality with the `init()` method.