Docs: Adjust existing instllation guides

[chriskthomas]

The installation guides are here: https://github.com/chriskthomas/linkfree-generator/tree/main/docs

Some need editing -- especially as new features like the ability to download your linkfree as a zip have simplified the setup for some providers.

[sayantan-2]

Can you specify the goal of index.md in the docs.

[sayantan-2]

Could you specify the goal of index.md in the docs.

[chriskthomas]

Could you specify the goal of index.md in the docs.

It's GitHub Pages magic that generates https://chriskthomas.github.io/linkfree-generator/ which is linked in the footer of the main site.