docs(dynamic pages): add an important warning

docs/fetching/dynamic.md

@@ -135,7 +135,7 @@ page = DynamicFetcher.fetch('https://example.com', proxy='http://username:passwo
 ### Proxy Rotation
 
 ```python
-from scrapling.fetchers import ProxyRotator
+from scrapling.fetchers import DynamicSession, ProxyRotator
 
 # Set up proxy rotation
 rotator = ProxyRotator([
@@ -153,6 +153,10 @@ with DynamicSession(proxy_rotator=rotator, headless=True) as session:
     page3 = session.fetch('https://example3.com', proxy='http://specific-proxy:8080')
 ```
 
+!!! warning
+
+    Remember that by default, all browser-based fetchers and sessions use a persistent browser context with a pool of tabs. However, since browsers can't set a proxy per tab, when you use a ProxyRotator, the fetcher will automatically open a separate context for each proxy, with one tab per context. Once the tab's job is done, both the tab and its context are closed.
+
 ### Downloading Files
 
 ```python