Cant't change the name of main html file in the output of `nim doc`?

[monsoonman]

I misspoke. Even after moving the `data` folder out of the source tree, the 
main html file remains to be `bmo.html` and not `index.html`. I got confused 
because `bmo.html` was changed to `index.html` by `nimble` task. I'have updated 
the previous post.