Moved extra docs out of quickstarts

.../guides/handling_data/using_nus_gitlab_instance/_index.md

..._nus_gitlab_instance/setting_up_gitlab_on_hcc_clusters.md

content/guides/running_applications/fortran_c_on_hcc.md

content/guides/submitting_jobs/condor_jobs_on_hcc.md

content/quickstarts/how_to_setup_x11_forwarding.md

content/quickstarts/mpi_jobs_on_hcc.md