Add link SPDX License List

[bact]

Make it more convenient for the spec readers

• For "SPDX License List", add link to https://spdx.org/licenses/
• For "SPDX Exceptions List", add link to https://spdx.org/licenses/exceptions-index.html
• For "custom-defined license", add link to https://spdx.github.io/spdx-spec/v3.0/model/ExpandedLicensing/Classes/CustomLicense/
• Add <..> around bare URLs in License profile to make it clickable on mkdocs

[swinslow]

Hi @bact, thanks for this!

One comment: Please note that a "custom-defined license" is different from a license expression:

• A license expression is a string representation of one or more licenses, potentially combined using "AND" / "OR" and similar operators.
• A "custom-defined license," in the sense used here, is a single license that is not on the SPDX License List. That custom-defined license might be represented in the SPDX 3.0 object model as a CustomLicense; or it might be represented in the license expression syntax as a LicenseRef- license (as described in some parts of the Annex D that you linked to).

So I probably wouldn't suggest linking to the license expression syntax annex for that item; probably best to link to the CustomLicense class.

Other than that, I'm generally +1 to this PR (though I note that it includes a couple of edits to serialization/rdf.md which are beyond the scope of the license-related profiles, so @zvr or @goneall may want to take a quick look at that also).

[bact]

Thanks @swinslow for clarification. I will revise accordingly based on your suggestions.

[bact]

Updated per @swinslow suggestions.

• "custom-defined license" now links to https://spdx.github.io/spdx-spec/v3.0/model/ExpandedLicensing/Classes/CustomLicense/
• Also links "SPDX Exceptions List" to https://spdx.org/licenses/exceptions-index.html