[Feature]: Add support for local feeds

[tylernku]

When I try to add a local rss file to nom it gives an error about unsupported protocol scheme. It would be really cool to have file:// protocol support.

[guyfedwards]

@tylernku Are you looking for something like nom ./myfeed.xml to parse and read a feed you might have downloaded from elsewhere (e.g. curl -O feeds.com/myfeed.xml)?

Any examples of usecase or files would be great, thanks.

[guyfedwards]

Just thinking about it, another option would just be to support file:// in nom add ... and just have it in the list along with other remote feeds

[tylernku]

my use case is pulling a bunch of youtube feeds from an invidio.us instance, combining them into a single .rss file and then (at the moment) navigating that local feed through newsboat. The main reason I actually did/do it that way was because it didn't seem like there was a way to get a combined feed view on newsboat, and if you're using rss feeds for youtube "subscriptions" it's a nice feature to have. The way that it does it is with the "file://" protocol which is probably a weird use case, but I can imagine it being useful to someone else.