[DOC]: Footnote markers render literally on the cuda.bindings install page #3384

Problem

install.rst uses Markdown-style footnotes ([^1], [^2], [^3]) in a reST file. reST does not parse that syntax, so the markers and the footnote text render as literal text instead of linked footnotes.

This predates 13.5.0 and is also present in 13.4.4.

Plan of action

1. Replace the markers with reST footnotes: auto-numbered references ([#]_) in the list, and matching .. [#] definitions at the end of the section.
2. Build the docs and confirm the references link to the footnote text and nothing renders literally.
3. Check the other install pages in the repo for the same Markdown-footnote pattern.