Docs about how to upgrade to the next major version

There are quite a few binary breaking changes in 4.0 so some of your code may not compile and will need to be fixed up. Apart from that, version 4.0.0 requires either net5.0 or .NETCoreApp 3.1. A functional breaking change is that Smidge now supports proper file globbing patterns so if you were using old syntax like: "~/Js/OtherFolder*js" to refer to all JS files in a folder, you would instead use file globbing patterns like: "~/Js/OtherFolder/*.js"

To upgrade from 1.x to 2.0 the biggest change is where you declare your bundles. In 1.x you declared your bundles in the services.AddSmidge declaration, in 2.0 this has changed and is more inline with how ASP.Net MVC configures it's routes. Bundles aren't part of the services so it doesn't make much sense to have them declared when you are configuring your services, so instead this is now done in app.UseSmidge, the docs have been updated to show the syntax.

There's quite a few API breaking changes but unless you were really tinkering around with the internals, this shouldn't affect you. If you made your own IPreProcessor, that signature has changed and you need to ensure you call the next IPreProcessor in the chain - see source code for examples of the correct usage.