Consider adding new documentation_url to Package model

[pombredanne]

See for instance https://github.com/aboutcode-org/scancode-toolkit/pull/4089/files#diff-b4834f0615d89ed1444ea5432c60661d3166082bdfd35986a028ba51c4305ea8R180
conda packages have it

[AyanSinhaMahapatra]

Also there in:

• Cargo: See https://github.com/aboutcode-org/scancode-toolkit/blob/develop/src/packagedcode/cargo.py#L219
• Java manifests: https://github.com/aboutcode-org/scancode-toolkit/blob/develop/src/packagedcode/jar_manifest.py#L349

And likely in other package ecosystems too. We should also do a pass of the manifests specs for each ecosystem and see if this is something we can add there.

[Dhruv276R]

@pombredanne I would like to contribute. Can you elaborate more on this?

[TanayPawar]

@pombredanne I would love to contribute to this issue. i want to know more about it.