add topics

[Beliavsky]

I suggest adding the topics uml, fortran, modern-fortran to the About section at https://github.com/t2time/ForUML.

[rouson]

@Beliavsky good suggestion. I'm not sure whether this project continues to be maintained. The most recent commit is from 2016. As an alternative, I recommend using PlantUML package in the Atom editor. Although it's not automated like ForUML, it has a couple of nice benefits:

1. It's sufficiently lightweight that diagrams can be constructed and updated quickly.2.
2. It's based on a scripting language that has a nice resembles a UML diagram even when viewed in raw text format.