Add llms subdir + update README (#145)

* add llms subdir + update README

* nits

* use same pre-commit as mlx

* update readmes a bit

* format

llms/phi2/README.md

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+# Phi-2
+
+Phi-2 is a 2.7B parameter language model released by Microsoft with
+performance that rivals much larger models.[^1] It was trained on a mixture of
+GPT-4 outputs and clean web text.
+
+Phi-2 efficiently runs on Apple silicon devices with 8GB of memory in 16-bit
+precision.
+
+## Setup 
+
+Download and convert the model:
+
+```sh 
+python convert.py
+```
+
+This will make the `weights.npz` file which MLX can read.
+
+> [!TIP] Alternatively, you can also download a few converted checkpoints from
+> the [MLX Community](https://huggingface.co/mlx-community) organization on
+> Hugging Face and skip the conversion step.
+
+
+## Generate 
+
+To generate text with the default prompt:
+
+```sh
+python phi2.py
+```
+
+Should give the output:
+
+```
+Answer: Mathematics is like a lighthouse that guides us through the darkness of
+uncertainty. Just as a lighthouse emits a steady beam of light, mathematics
+provides us with a clear path to navigate through complex problems. It
+illuminates our understanding and helps us make sense of the world around us.
+
+Exercise 2:
+Compare and contrast the role of logic in mathematics and the role of a compass
+in navigation.
+
+Answer: Logic in mathematics is like a compass in navigation. It helps
+```
+
+To use your own prompt:
+
+```sh
+python phi2.py --prompt <your prompt here> --max_tokens <max_tokens_to_generate>
+```
+
+To see a list of options run:
+
+```sh
+python phi2.py --help
+```
+
+[^1]: For more details on the model see the [blog post](
+https://www.microsoft.com/en-us/research/blog/phi-2-the-surprising-power-of-small-language-models/)
+and the [Hugging Face repo](https://huggingface.co/microsoft/phi-2)