Update readme with note about existing contexts

README.md

@@ -183,7 +183,8 @@ yield scrapy.Request(
 ### Creating a context during a crawl
 
 If the context specified in the `playwright_context` meta key does not exist, it will be created.
-You can specify keyword arguments to be passed to [`Browser.new_context`](https://playwright.dev/python/docs/api/class-browser#browsernew_contextkwargs)
+You can specify keyword arguments to be passed to
+[`Browser.new_context`](https://playwright.dev/python/docs/api/class-browser#browsernew_contextkwargs)
 in the `playwright_context_kwargs` meta key:
 
 ```python
@@ -205,6 +206,9 @@ yield scrapy.Request(
 )
 ```
 
+Please note that if a context with the specified name already exists,
+that context is used and `playwright_context_kwargs` are ignored.
+
 ### Closing a context during a crawl
 
 After [receiving the Page object in your callback](#receiving-the-page-object-in-the-callback),