Add installation and usage instructions

Closes #6

README.md

@@ -1,3 +1,64 @@
 # 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`.
+
+There are several additional options available:
+
+- `--context` allows you to provide one or more text files as context for your chat, which is sent as an initial system message at the start of the conversation. You can provide the argument multiple times to add multiple files.
+- `--name` gives your chat session a name. This is used to name the history file.
+
+See `llm chat --help` for a full description of all options and their usage.
+
+Finally, you can load a previous chat session using the `llm load` command. For example:
+
+```bash
+llm load /path/to/session.json
+```
+
+See `llm load --help` for more information.