Modify "The AUTHORS.md file" section in packaging/structure.html

[PipKat]

Description of the modifications

Based on a recent PyAnsys developer's meeting, the AUTHORS.MD file use is for ANSYS, INC. and possibly external contributors who request that they be added. Update this section and add a "The CONTRIBUTORS.MD file" section. to explain how it is a list of names for maintainers and contributors.

Useful links and references

https://dev.docs.pyansys.com/packaging/structure.html

[RobPasMue]

Ah, good call @PipKat! As soon as ansys/pyansys-geometry#561 is merged, I'll get to this

Thanks for opening the issue! =)

[RobPasMue]

Working on this!