Incomplete documentation for add_js_file() and add_css_file()

[mgeier]

Describe the bug

• The examples do not include the CRC32 checksums added in Append CRC32 checksum to asset URIs #11415
• There should be a "changed in version 7.1" mentioning those checksums (https://www.sphinx-doc.org/en/master/changes.html#release-7-1-0-released-jul-24-2023)
• There should be a hint how JS/CSS files can be copied to the _static directory (see also Adding CSS and javascript files from extensions #11173 (comment))
• It might also be helpful to mention that site authors (as opposed to extension developers) can use the config values html_js_files and html_css_files in combination with html_static_path?
• Maybe it could even be mentioned that files specified by extensions can be overridden by site authors by simply putting a file with the same name into their html_static_path (which currently doesn't fully work: Regression: CSS file added by extension cannot be overridden by users anymore #12096)?

How to Reproduce

Look at https://www.sphinx-doc.org/en/master/extdev/appapi.html#sphinx.application.Sphinx.add_js_file and https://www.sphinx-doc.org/en/master/extdev/appapi.html#sphinx.application.Sphinx.add_css_file.