Add contributing guideline to the repo

Would be nice to have the contributing file with some instructions how someone can help improve the website and also how the page is being developed.

changed due date to May 01, 2020

added 6. low-priority label

changed due date to October 31, 2020

Added a label and a deadline.

added 5. feature proposal label

removed 5. feature proposal label

removed due date

added 1. on hold + 1 deleted label

removed 6. low-priority label

unassigned @sidorela

@sidorela do you think @irisftw can take this over?

I have created an initial file with instructions which can be improved.

closed