C++ requirements?

[Flamefire]

https://www.boost.org/doc/libs/1_86_0/libs/spirit/doc/x3/html/index.html reads

Spirit X3 in Boost 1.81 (scheduled to November 2022) will use C++17 features.

Same in the repo readme.

That should be updated to at least reflect a future Boost or state that C++17 is now required.