Link to Purl Version Specification does not work

[weichslgartner]

The link to the purl version range defined in

specification/schema/bom-1.5.xsd

Line 3647 in 8af880d

<xs:documentation>A version range specified in Package URL Version Range syntax (vers) which is defined at https://github.com/package-url/purl-spec/VERSION-RANGE-SPEC.rst</xs:documentation>

(https://github.com/package-url/purl-spec/VERSION-RANGE-SPEC.rst) does not work at the moment.

Currently the Version-Range Spec is not merged to main but only available in a different branch:
https://github.com/package-url/purl-spec/blob/version-range-spec/VERSION-RANGE-SPEC.rst

Once the spec is merged the problem should resolve by itself, but in the meantime it is a dead link.

[jkowalleck]

duplicates #311, #399 & related to #187