docs(computer-use): document requesting the actual screenshot on chat surfaces

Follow-up to PR #90183 — computer_use now saves a bounded shareable copy of
image captures, so attachment-capable surfaces (Telegram, Discord, Desktop)
can deliver the real screenshot when the user asks. Documents the behavior,
the 20-file cache bound, and the no-automatic-send rule.

website/docs/user-guide/features/computer-use.md

@@ -284,6 +284,23 @@ the model substitutes the platform's idiomatic shortcut and app name):
 During all of this, your cursor stays wherever you left it and the email
 app never comes to front.
 
+## Receiving the actual screenshot
+
+Screenshots taken during computer control are normally internal — they exist
+so the model can see the screen, and the agent replies in text. But every
+image capture also saves a bounded, shareable copy under Hermes' image cache
+and reports its path, so on attachment-capable surfaces (Telegram, Discord,
+Desktop, and other gateway platforms) you can simply ask:
+
+> *"Send me a screenshot of my screen."*
+
+and the agent delivers the real image as a native attachment, not just a
+description. On the CLI there is no attachment channel, so the agent gives
+you the saved file's path instead.
+
+Only the 20 most recent capture files are kept, and screenshots are never
+sent automatically — only when you ask for one.
+
 ## Provider compatibility
 
 | Provider | Vision? | Works? | Notes |