doc: document options panel, entry points, and the ChatGPT prefill limitation

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

README.md

@@ -12,6 +12,46 @@ This is an unofficial extension provided by Zavage Software Inc.
 
 See `LICENSE.txt` for licensing terms.
 
+## Options
+
+Open `about:addons`, select this extension, and choose the **Options** tab
+(**Preferences** on macOS and Linux). Available settings:
+
+- **Model** *(experimental)* — a model slug such as `auto`. ChatGPT may ignore
+  it and use your account default; leave blank to always use the account
+  default.
+- **Request a temporary chat** — asks ChatGPT not to save the conversation.
+  ChatGPT may not honour this; check its own indicator before relying on it.
+- **Ask ChatGPT to use web search** — a hint to ChatGPT's interface, not a
+  guarantee.
+- **Open in** — a new tab, a new background tab, or a new window.
+- **Prompt template** — wraps your text, for example `Explain simply: {query}`.
+
+These settings apply to the new entry points: selecting text and choosing
+**Ask ChatGPT** from the right-click menu, or pressing
+<kbd>Alt</kbd>+<kbd>Shift</kbd>+<kbd>G</kbd>. Rebind the shortcut under
+**Manage Extension Shortcuts** in the Add-ons gear menu.
+
+The `gpt <query>` address-bar search is unchanged and does not read these
+settings.
+
+The options panel, the right-click item, and the keyboard shortcut require
+Firefox 112 or newer. On older versions the extension still installs and the
+`gpt <query>` address-bar search still works; only these newer features are
+inactive.
+
+## Why you press Enter twice
+
+ChatGPT no longer submits prompts that are passed to it in a URL — it fills them
+into the composer and waits. So `gpt <query>` opens ChatGPT with your query
+filled in, and you press Enter there to send it.
+
+This is a change OpenAI made to chatgpt.com, not a fault in this extension, and
+it is outside our control. It was a deliberate security measure: automatically
+running a prompt that arrived in a link let malicious links execute instructions
+in a signed-in ChatGPT session. The extra keypress is the checkpoint that
+prevents that. No API key, server, or intermediary is involved either way.
+
 ## Browser Support
 
 Firefox Desktop is the current development and release target. Chrome, Brave,
@@ -44,4 +84,14 @@ configured in Firefox search settings.
 
 ## Privacy Policy
 
-This extension collects zero user data.
+This extension has no server, no API key, and no intermediary. Nothing is
+reported to Zavage Software.
+
+- Your settings are stored in your own browser profile. If you use Firefox Sync
+  with **Add-ons** enabled, they sync end-to-end encrypted through your own
+  Mozilla account.
+- When you choose **Ask ChatGPT** or press the shortcut, the text you selected
+  is placed in the chatgpt.com URL the extension opens for you. It goes nowhere
+  else.
+- The extension reads a page's selected text only at the moment you invoke it,
+  and never reads page addresses or titles.