The README names what the project covers and where it runs
A reader’s first question is whether they are in the audience at all. A README that describes what the project does but never names the forges, registries, runtimes, or platforms it supports makes every reader run the install command to find out, and most of them will not.
Observable check
README.md names the platforms, forges, ecosystems, registries, or runtimes the project supports, and each name it claims appears in the source, the manifest, or the CI configuration.