doc: surface the sign-in and send hint

ChatGPT can require signing in, and it does not always send a prefilled
prompt. The README and options panel mentioned pressing Enter only in
passing. Give both a prominent note covering sign-in and Enter or Send,
and drop the inline mentions it replaces.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

README.md

@@ -4,6 +4,9 @@ This extension adds ChatGPT as a configurable Firefox search provider. Type
 `gpt <query>` in the address bar to open the query in a new ChatGPT session.
 It uses no API key, custom server, or intermediary handler.
 
+**ChatGPT may require you to sign in. If your prompt is not sent automatically,
+press Enter or click Send in ChatGPT.**
+
 This is an unofficial extension provided by Zavage Software Inc.
 
 - [Firefox Add-ons listing](https://addons.mozilla.org/en-US/firefox/addon/search-with-chatgpt/)
@@ -17,9 +20,8 @@ See `LICENSE.txt` for licensing terms.
 ## Ask about selected text
 
 Highlight text on a webpage, right-click it, and choose **Ask ChatGPT**.
-ChatGPT opens with your selection. If the prompt is not sent automatically,
-press Enter in ChatGPT to send it. Try selecting a paragraph you want explained or
-translated.
+ChatGPT opens with your selection. Try selecting a paragraph you want explained
+or translated.
 
 You can also press **Alt+Shift+G** to use the current selection. With nothing
 selected, the shortcut opens a blank chat. Change the shortcut under
@@ -106,7 +108,8 @@ inactive.
 
 The extension opens ChatGPT with the prompt in the URL. ChatGPT controls what
 happens next: it may send the prompt automatically or leave it in the composer.
-**If the prompt is not sent automatically, press Enter in ChatGPT.**
+You may need to sign in before continuing. **If your prompt is not sent
+automatically, press Enter or click Send in ChatGPT.**
 
 If ChatGPT shows a verification error, try signing in and opening the prompt
 again. Signing in has helped in testing, but does not guarantee automatic