docs(versioning/semver): rewrite readme (#29868)

Co-authored-by: Sebastian Poxhofer <secustor@users.noreply.github.com>

lib/modules/versioning/semver/readme.md

-Renovate's Semantic Versioning is a strict/independent implementation of [Semantic Versioning 2.0](https://semver.org). It has been developed to be used in situations where exact-only SemVer support is needed and not npm's extended semver implementation including ranges.
+Renovate's `semver` versioning _strictly_ implements the [Semantic Versioning 2.0](https://semver.org) specification.
+Because the SemVer 2.0 specification does _not_ allow ranges, Renovate's `semver` versioning also does _not_ support ranges.
 
-Ranges are not supported, in line with the specification.
+Only use the `semver` versioning when you mean to follow the full SemVer 2.0 specifications strictly.
+If you need a more forgiving variant use `semver-coerced`.