docs: clarify network aliases and add section on tld management
docs: clarify network aliases and add section on tld management

Closes #3995

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dokku/dokku,progrium/dokku,progrium/dokku,progrium/dokku,dokku/dokku,claytonbrown/dokku,claytonbrown/dokku,progrium/dokku,progrium/dokku,dokku/dokku,claytonbrown/dokku,dokku/dokku,claytonbrown/dokku,claytonbrown/dokku,claytonbrown/dokku,dokku/dokku,progrium/dokku,claytonbrown/dokku,dokku/dokku,dokku/dokku,progrium/dokku,dokku/dokku,progrium/dokku,claytonbrown/dokku