Added support-us page with all donation info

Not perfect, but I think it's a good start. The payment form in the "Donate" section redirects to our Dolibarr server. The "become a member" button redirects to the corresponding Dolibarr form.

The donation integration with Dolibarr is really bad (nothing is tracked :s), however, the membership part is working as expected, so I tend to think this is good enough to get started.

Let me know what you think about it :)