Add troubleshooting for WSL and hugo server

[gdog2u]

I recently came across the same issue as describe in Hugo issue #9809. This issue is that when using Hugo from WSL, and your files are on Windows, Hugo cannot detect file changes the same way as if both parts are on the the same system (both on WSL or both on Windows)

The resolution for this was to use the --poll flag to better enable Hugo's watcher to catch changes.

This was not obvious to me, and took me quite some time to find, as it's only mentioned in a github issue. I believe this should at least be mentioned in the troubleshooting docs, so as to make it easier to find this information.

I'd submit it as PR, but I don't feel that I know enough about the technical details, or correct verbiage to do so.