readme : add link to Autopen under UIs (#11684)

Autopen (https://github.com/blackhole89/autopen) is a graphical text editor that uses llama.cpp to tokenize the buffer on the fly, score the buffer, visualise token logits and allow you to switch back and forth between different possible completions at any point. It hopefully meets the criteria for inclusion, as the dependency on llama.cpp is stated prominently.

README.md

@@ -189,6 +189,7 @@ Instructions for adding support for new models: [HOWTO-add-model.md](docs/develo
 - [ramalama](https://github.com/containers/ramalama) (MIT)
 - [semperai/amica](https://github.com/semperai/amica) (MIT)
 - [withcatai/catai](https://github.com/withcatai/catai) (MIT)
+- [Autopen](https://github.com/blackhole89/autopen) (GPL)
 
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