Adding geometries OT807_IT745 and OT807_IT746

[valeguglia]

The layouts of the geometries can be found in https://vvaguglie.web.cern.ch/www/layouts/OT807_IT746/ and https://vvaguglie.web.cern.ch/www/layouts/OT807_IT745/

[alkemyst]

Hello,
thanks for this.
I have one change request: whenever we create new geometries, it would be mandatory to add a description at the end of readme.txt. This description should clearly state which geometry the new version is based on, so that we can track the genealogy of geometries and document all differences between parent and derived versions.