Add limitations to readme file

Author: maximejobin

README.md

@@ -19,6 +19,7 @@ This project is sponsored by SatelliteWP, a [WordPress maintenance service](http
   1. [Installation](#installation)
   1. [Configuration](#configuration)
   1. [Debug](#debug)
+  1. [Limitations](#limitations)
   1. [FAQ](#faq)
   1. [License](#license)
 
@@ -176,6 +177,21 @@ Reasons for not serving a cached file:
   * **Specific mobile cache activated**: If you activated specific cache (one for mobile and one for desktop) in WP Rocket, HTML files (pages, posts, ...) won't be served directly because Rocket-Nginx cannot know if the request was made by mobile or desktop device.
   * **File not cached**: No cached file was found for that request.
 
+## <a name='limitations'>Limitations</a>
+Is Rocket-Nginx perfect? No, it's not! We tried to make it as perfect as possible, but Nginx's scripting language does not offer all possibilities offered by a language like PHP, for instance. Therefore, there are some limitations.
+
+❌**Cache for mobile devices**
+
+Short answer: Rocket-Nginx won't manage any request if you activate the [Mobile cache feature](https://docs.wp-rocket.me/article/708-mobile-cache).
+
+In today's world, we usually use a responsive theme that will adapt to your visitor's screen. Therefore, activating the 'cache for mobile device' to create a separate cache for mobile is not needed. It's useless as the same code will be cached twice. That being said, there are cases where the code is different and you might want to use that option. Unfortunately, knowing if the device is a mobile or not is as simple as you might think. There are so many devices and browsers to handle! The Nginx's scripting language is not powerful enough to achieve the validation correctly. Therefore, if you activate this feature, Rocket-Nginx will let WP Rocket handle the device validation and serve the cached page.
+
+❌**WEBP Compatibility**
+
+Short answer: Rocket-Nginx won't serve the WebP caching files generated by WP Rocket if you activate the [WebP Compatibility feature](https://docs.wp-rocket.me/article/1282-webp).
+
+WP Rocket is able to create a specific cache if you used a tool to convert your images (JPG, PNG, ...) to WebP. Unfortunately, the Nginx's scripting language is not powerful enough to achieve the validation correctly. Therefore, if you activate this feature, Rocket-Nginx will let WP Rocket handle the request and serve the right cached page, depending on the context.
+
 ## <a name='faq'>FAQ</a>
 
 **<a name='faq_bfcache'>Is Rocket-Nginx compatible with BF Cache (Back/forward cache)?</a>**