Document available themes

[applejag]

Describe the bug
You mention that you support themes in the README, but the only thing you view is the following:

Change the color theme.

freeze artichoke.hs --theme dracula

Never in the docs or the code base can I see which themes you support.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://github.com/charmbracelet/freeze?tab=readme-ov-file#theme
2. Look around the codebase
3. Sadface

Expected behavior
After looking at your dependencies, I could quite quickly see that you're using chroma.

Chroma does link to a page where you can view themes, so it'd be nice to have the same link here in the freeze docs: https://xyproto.github.io/splash/docs/index.html

You also add the "charm" specific theme, which is not included in that page. So maybe something like:

As we use chroma, you can use any of the themes found in https://github.com/alecthomas/chroma/tree/master/styles.
Previews of chroma's themes: https://xyproto.github.io/splash/docs/index.html

We also add in an additional charm theme

Screenshots
N/A

Desktop (please complete the following information):

• OS: linux
• Browser firefox
• Version 124.0.1

Smartphone (please complete the following information):
N/A

Additional context
Nice tool you got here :) I really like it

[rennsax]

Thanks for this issue, or I'll never find the available theme list 😂.

For those we come to this issue in the future, TL;DR: see this page.

[meleu-cw]

And for those who come to this issue wanting to compare all themes in one page, check this link here.