README: Hide authinfo explanation, update Claude 3.7 info

* README.org (Claude 3.7 support, authinfo): Hide authinfo
details.  This is causing more confusion than clarity as readers are
faced with two unfamiliar systems (gptel and authinfo
configuration) instead of one.

Update the Claude 3.7 thinking support text -- using a separate
Anthropic backend for this model is now the official solution, as
no Anthropic-only user options are planned for now to set this.

Author: karthink

README.org

@@ -93,7 +93,6 @@ gptel uses Curl if available, but falls back to the built-in url-retrieve to wor
   - [[#setup][Setup]]
     - [[#chatgpt][ChatGPT]]
     - [[#other-llm-backends][Other LLM backends]]
-      - [[#optional-securing-api-keys-with-authinfo][(Optional) Securing API keys with =authinfo=]]
       - [[#azure][Azure]]
       - [[#gpt4all][GPT4All]]
       - [[#ollama][Ollama]]
@@ -214,14 +213,17 @@ Once this backend is registered, you'll see model names prefixed by "Claude:" ap
 
 See below for details on your preferred LLM provider, including local LLMs.
 
-**** (Optional) Securing API keys with =authinfo=
+#+html: <details><summary>
+***** (Optional) Securing API keys with =authinfo=
+#+html: </summary>
 
 You can use Emacs' built-in support for =authinfo= to store API keys required by gptel.  Add your API keys to =~/.authinfo=, and leave =gptel-api-key= set to its default.  By default, the API endpoint DNS name (e.g. "api.openai.com") is used as HOST and "apikey" as USER.
 #+begin_src authinfo
 machine api.openai.com login apikey password sk-secret-openai-api-key-goes-here
 machine api.anthropic.com login apikey password sk-secret-anthropic-api-key-goes-here
 #+end_src
 
+#+html: </details>
 #+html: <details><summary>
 **** Azure
 #+html: </summary>
@@ -534,7 +536,7 @@ The above code makes the backend available to select.  If you want it to be the
 
 ***** (Optional) Interim support for Claude 3.7 Sonnet
 
-gptel does not yet support specifying LLM "reasoning"/"thinking" behaviors dynamically through its interface.  This effort is ongoing, but in the meantime you use the Claude 3.7 Sonnet model in its "thinking" mode by defining a second Claude backend and selecting it in via the UI or elisp:
+To use Claude 3.7 Sonnet model in its "thinking" mode, you can define a second Claude backend and select it via the UI or elisp:
 
 #+begin_src emacs-lisp
 (gptel-make-anthropic "Claude-thinking" ;Any name you want
@@ -553,7 +555,7 @@ gptel does not yet support specifying LLM "reasoning"/"thinking" behaviors dynam
 
 You can set the reasoning budget tokens and max tokens for this usage via the =:budget_tokens= and =:max_tokens= keys here, respectively.
 
-Once proper support for specifying reasoning behaviors is added to gptel's UI this will be unnecessary.
+You can control whether/how the reasoning output is shown via gptel's menu or =gptel-include-reasoning=, see [[#handle-reasoning-content][handling reasoning content]]. 
 
 #+html: </details>
 #+html: <details><summary>