Standardising relative pathnames: Security Best Practices + maybe elsewhere

[rphair]

Fixes problem reported here on Discord.

TL;DR: Some link syntaxes seem browser dependent & this is an attempt to standardise on a known working syntax for some material I wrote before some standards about inter-document linking were more rigorously applied.

For the link to Installing the node from source here, on the live site I've seen it open correctly with the URL into a new window but fail when simply clicking on the link.

• To me this suggests something on the front end is interpreting the links (and likely not correct for me & my JS blocker) and sometimes getting it wrong when the Docusaurus source begins with .. or a relative pathname that doesn't begin with docs (although /docs seems to work just as well).

I've standardised the Security Best Practices pages which I wrote long ago & which had a hodgepodge of syntaxes, including the Air Gap link to the "Install from source" page that was reported broken above. I've concluded linking to docs/.../<filename>.md is canonical because output from this comment generally shows that syntax:

grep '](' `find docs -type f -name \*.md` | grep -v http | grep -v static.img | grep -v '(#' | grep -v cardano-improvement-proposals | grep '(.*)'

after repeated, recent edits by @CarlosLopezDeLara @gufmar on these files which have the most intra-Portal links: and so they are especially welcome to check the syntax changes here. (There are some other edits to bring the content up to date.)