Add contributing guide
Copy of DCO + License section from GitLab Pages contributing guide https://gitlab.com/gitlab-org/gitlab-pages/-/blob/2e9bd40bd61de95cbb8c7e598c71753d3f7475cb/CONTRIBUTING.md
Related to #1 (closed)
Edited by Jaime Martinez
Copy of DCO + License section from GitLab Pages contributing guide https://gitlab.com/gitlab-org/gitlab-pages/-/blob/2e9bd40bd61de95cbb8c7e598c71753d3f7475cb/CONTRIBUTING.md
Related to #1 (closed)