"Reference" as button for the main menu navigation in the header

[sebastian-loos]

@larnsce and @mianzg

I was just asking myself if [Function Refernce](https://openwashdata.github.io/wasteskipsblantyre/reference/index.html) is the right title for this page?

Wouldn't "data sets" or something similar be more appropriate?

Either way, I'm not sure how much can/should do about it. According to an open issue from (2022-08) in the pkgdown repo we would have to provide a custom template for this page.

[larnsce]

Thanks, @sebastian-loos. That's a great observation and I would also like to fix that. I will add it to the tasks for openwashdata-dev/openwashdata#8