clarify licensing

[magicmark]

prior art: https://github.com/graphql/graphql-scalars?tab=readme-ov-file#licensing
do we need to copy that whole thing verbatim though? or can we just add a pointer to this section in graphql/graphql-spec?

fwiw related prior art:

• https://agentclientprotocol.com/rfds/about#licensing

[benjie]

Licensing will be governed by the project charter; essentially the same as all our other WGs:

https://github.com/graphql/graphql-wg/blob/main/membership/GraphQL-Specification_Membership-2021-01-25-PREVIEW.pdf

MIT for code, OWFa1.0 for specs, © GraphQL Contributors.

I'm working with LF to get this finalized.