* Update mesh_gateway.html.md * Apply suggestions from code review Co-Authored-By: Luke Kysow <1034429+lkysow@users.noreply.github.com> * Add WAN joining requirement * re-word primary dc guidance Co-Authored-By: Luke Kysow <1034429+lkysow@users.noreply.github.com> * Update website/source/docs/connect/mesh_gateway.html.md