added lincensing

Dear All,

I just wanted to add a page where we would add our licensing strategy for our material. For the time being I copied/pasted the last slide of our discussion in June. https://indico.cern.ch/event/1158301/contributions/4863934/attachments/2440193/4180418/SoftwareLicense.pdf but maybe one should be a bit more clear?!

I let you judge if to merge it and add it to the website, or not...