[FEAT] Align doc file/folder names with site

[zslade]

Is your proposal related to a problem?

Sometimes it can be hard to find the right markdown file in the docs to update because their names don't always align with their page names on the Splink site.

Describe the solution you'd like

Update the names of the files and folders in the splink/docs directory so that they align (as much as reasonably possible) with the website. When it make sense to shorten longer site page names, keeping the first word in the page name at least would help with navigation.

Describe alternatives you've considered

Additional context