Include links to the mailing lists on the Contact us page

The contact us page should include links to the subscription pages for the nmaas-annouce and nmaas-users mailing lists, along with an appropriate description:

• https://lists.geant.org/sympa/info/nmaas-announce (low frequency nmaas news)
• https://lists.geant.org/sympa/info/nmaas-users (users discussion about nmaas)