MainWP + Nginx Webserver

[kwcjr (Keith Crain)]

@Olli-MainWP There are no known conflicts with any server software. Our test servers run on nginx, MySQL
Currently the only known caveat with MariaDB is the MainWP Maintenance Extension but this would effect Child Sites not the MainWP Installation if it causes issues at all

@bogdan

Based on user experience, OPTIMIZE command that is used for optimizing database sometimes in very rare cases caused problems with MariaDB DBs. We felt that we need to warn users.