Added static_bundled_build feature, imported readme into the crate documention

[VictorKoenders]

From the fermium documentation:

If you use the static_bundled_build cargo feature then this will build SDL2 using a bundled copy of the source and then statically link to that. Building SDL2 can take a bit during that first build (usually 1 minute or more).

Makes us windows developers' lives a bit easier

[17cupsofcoffee]

Seems reasonable! I tend to just dump the SDL2 files into my project when I create it, so dunno if I'll use this personally, but it doesn't hurt to have.

All of the SDL stuff might have to be tweaked when SDL3 lands anyway - I have no clue if/when sdl2 or fermium are going to get updated to support that,..