Add installation and usage instructions

Closes #6

README.md

@@ -1,3 +1,49 @@
 # LLM Chat
 
-A general CLI interface for large language models.
+This project is currently a CLI interface for OpenAI's [GPT model API](https://platform.openai.com/docs/guides/gpt). The long term goal is to be much more general and interface with any LLM, whether that be a cloud service or a model running locally.
+
+## Usage
+
+### Installation
+
+The package is not currently published so you will need to build it yourself. To do so you will need [Poetry](https://python-poetry.org/) v1.5 or later. Once you have that installed, run the following commands:
+
+```bash
+git clone https://code.harrison.sh/paul/llm-chat.git
+cd llm-chat
+poetry build
+```
+
+This will create a wheel file in the `dist` directory. You can then install it with `pip`:
+
+```bash
+pip install dist/llm_chat-0.6.1-py3-none-any.whl
+```
+
+Note, a much better way to install this package system wide is to use [pipx](https://pypa.github.io/pipx/). This will install the package in an isolated environment and make the `llm` command available on your path.
+
+### Configuration
+
+Your OpenAI API key must be set in the `OPENAI_API_KEY` environment variable. The following additional environment variables are supported:
+
+| Variable             | Description                                                        |
+| -------------------- | ------------------------------------------------------------------ |
+| `OPENAI_MODEL`       | The model to use. Defaults to `gpt-3.5-turbo`.                     |
+| `OPENAI_TEMPERATURE` | The temperature to use when generating text. Defaults to `0.7`.    |
+| `OPENAI_HISTORY_DIR` | The directory to store chat history in. Defaults to `~/.llm_chat`. |
+
+The settings can also be configured via command line arguments. Run `llm chat --help` for more information.
+
+### Usage
+
+To start a chat session, run the following command:
+
+```bash
+llm chat 
+```
+
+This will start a chat session with the default settings looking something like the image below:
+
+![Chat session](./llm-chat.png)
+
+The CLI accepts multi-line input, so to send the input to the model press `Esc + Enter`. After each message a running total cost will be displayed. To exit the chat session, send the message `/q`.