Docs(#i3,i12): landing page links

[andybeet]

Justification

Broken links needed fixing and additional links to supporting resources and code base were needed.

fixes #3
fixes #12

Reviewer instructions:

In RStudio you can render the site by either:

1. quarto::quarto_render() - This will create a local folder called _site in the root of the project. This is the preferred method or
2. opening the index.qmd file in the root directory (of this branch) and click the blue render arrow.

• There is a new page in the appendix called known limitations
• The resources section has added links

[andybeet]

@jacobkasper Any comments?