Improve contributing

[akaszynski]

There's content duplication in the contributing section and it should match MAPDL's contributing section.

Also, should include what it takes to setup a development environment (e.g. installing DPF locally, etc.)

[PProfizi]

Hi @akaszynski, could you please pinpoint the sections where content is duplicated?
Also when you say it should match MAPDL's contributing section, are you talking about the structure of the page?