Update runners networking documentation
Part of https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/13710
Also, it's a follow-up for !3739 (comment 630344913)
Edited by Tomasz Maczukin
Part of https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/13710
Also, it's a follow-up for !3739 (comment 630344913)