Consider removing default values for lat/lon

[maneesha]

This template uses default values of (45, -1) for latitude and longitude. See https://github.com/carpentries/workshop-template/blob/gh-pages/index.md?plain=1#L10

This means that if people do not update these values, the page builds successfully, without any "FIXME" style placeholders. This means people may not realize these values need to be updated. Consider replacing the default values with something that either produces an error or makes it clear these are not valid values. Note that (0,0) are valid lat/lon coordinates so that would not work.