Release candidate 1 of version 2.0 of the SPDX Java Tools

What's Changed

• Update README for release by @goneall in #168
• Add instructions in README to convert to SPDX 3. by @vargenau in #171
• Add JSONLD to the documenation for supported file types by @goneall in #169
• Update to SPDX Spec 3.0.1 by @goneall in #173

Full Changelog: v2.0.0-Alpha...v2.0.0-RC1