Add SPDX 3.0 page

[bact]

• Add SPDX 3.0 page
• Note that this PR depends on the new crosswalk data after the merge of Add SPDX 3.0 + Update SPDX 2.3 crosswalks codemeta#429 (+ regeneration of the crosswalk.csv)

[progval]

I'd rather use "SBOM" for both, because "fields" does not describe anything specific to SPDX (all formats have fields)

[bact]

Thank you. Fixed as suggested.

[progval]

Note that this PR depends on the new crosswalk data after the merge of codemeta/codemeta#429 (+ regeneration of the crosswalk.csv)

Oops I missed this.