Add social proof to the site content

[artob]

Over the past 15 years, the initiative has seen a fair bit of success even without any active efforts on our part. The site copy (such as for #93) should highlight the social proof about the widespread adoption and increased acceptance of the Unlicense. For example, significantly, the Unlicense has gained an SPDX identifier somewhere along the way, and is included in packaging policies for various Linux and BSD distributions.

[mlinksva]

The SPDX identifier is from before 2016...seems to have been requested in 2012 https://lists.spdx.org/g/Spdx-legal/topic/22080280 and was added in SPDX License List v1.18 in 2013 https://lists.spdx.org/g/Spdx-legal/message/643

It appears there also exist some Unlicense variants https://github.com/spdx/license-list-XML/issues?q=unlicense