Building with SMESH

[marty-sullivan]

Really excited to test this package out!

Currently building pythonocc-core from source and would like to add the SMESH support. From what I can tell, if I add -DPYTHONOCC_WRAP_SMESH this is adding it to the build, but not sure if that's what you intended.

Can you just add a note to the INSTALL.md with your intended way to wrap SMESH during the build?