Where does list of licenses come from?

Hi,

I was playing with this code and to give one example, I found this license: https://github.com/google/licenseclassifier/blob/main/licenses/Facebook-2-Clause.txt
It says in your source code ( https://github.com/google/licenseclassifier/blob/148b633b0534b8cf7a143e54cdae2b9229a78a82/license_type.go#L26 ) that:

> The names come from the https://spdx.org/licenses website, and are also the filenames of the licenses in licenseclassifier/licenses.

I can't actually find this and certain other licenses on the SPDX website. Could you elaborate how you both maintain the list and how you found this on the SPDX site?

I think it's great that you have more licenses in here, but I just want to make sure there isn't a collision since the returned identifiers are meant to be unique. If these aren't actually in SPDX, are you willing to rename them or accept a patch to do so which adds the SPDX `LicenseRef-` prefixes? (These prefixes are there to specify non-SPDX licenses.)

Thanks!