Clarify where to put nginx custom template without `WORKDIR`
Clarify where to put nginx custom template without `WORKDIR`

Docker assume `/` as [default `WORKDIR`](https://docs.docker.com/engine/reference/run/#workdir), but dokku [looks in the `/app` folder](https://github.com/dokku/dokku/blob/master/plugins/common/functions#L257)

[ci skip]
Evlos/dokku,econya/dokku,alexquick/dokku,progrium/dokku,jimjag/dokku,claytonbrown/dokku,sseemayer/dokku,amaltson/dokku,Evlos/dokku,claytonbrown/dokku,dokku/dokku,johnfraney/dokku,Evlos/dokku,Evlos/dokku,codeconfab/dokku,expa/dokku,jimjag/dokku,alexquick/dokku,econya/dokku,progrium/dokku,jimjag/dokku,expa/dokku,expa/dokku,alexquick/dokku,econya/dokku,fruitl00p/dokku,alexquick/dokku,alexquick/dokku,econya/dokku,johnfraney/dokku,amaltson/dokku,claytonbrown/dokku,econya/dokku,dokku/dokku,econya/dokku,amaltson/dokku,elia/dokku,fruitl00p/dokku,johnfraney/dokku,amaltson/dokku,codeconfab/dokku,johnfraney/dokku,alexquick/dokku,expa/dokku,fruitl00p/dokku,progrium/dokku,fruitl00p/dokku,elia/dokku,sseemayer/dokku,econya/dokku,amaltson/dokku,codeconfab/dokku,fruitl00p/dokku,expa/dokku,claytonbrown/dokku,johnfraney/dokku,sseemayer/dokku,jimjag/dokku,amaltson/dokku,dokku/dokku,fruitl00p/dokku,expa/dokku,claytonbrown/dokku,codeconfab/dokku,Evlos/dokku,elia/dokku,elia/dokku,sseemayer/dokku,amaltson/dokku,dokku/dokku,expa/dokku,amaltson/dokku,dokku/dokku,sseemayer/dokku,fruitl00p/dokku,johnfraney/dokku,expa/dokku,dokku/dokku,dokku/dokku,Evlos/dokku,alexquick/dokku,progrium/dokku,dokku/dokku,johnfraney/dokku,jimjag/dokku,sseemayer/dokku,fruitl00p/dokku,jimjag/dokku,econya/dokku,progrium/dokku,codeconfab/dokku,codeconfab/dokku,sseemayer/dokku,progrium/dokku,claytonbrown/dokku,elia/dokku,jimjag/dokku,Evlos/dokku,elia/dokku,progrium/dokku,codeconfab/dokku,alexquick/dokku,Evlos/dokku,elia/dokku,claytonbrown/dokku,elia/dokku,progrium/dokku,claytonbrown/dokku,codeconfab/dokku,jimjag/dokku,johnfraney/dokku,sseemayer/dokku