Adds building instructions for fedora

I spend a good time until I could run the examples on Fedora with this library. I think this addition to the README can help other fedora user.

Lists needed packages for fedora and provides help for the static linking error on SDL2 during building on fedora.

This command for example

cargo run --example simple

produces this output without specifying the Rustflags:

error: could not find native static library `SDL2main`, perhaps an -L flag is missing?

error: could not compile `sdl2-sys` (lib) due to previous error
warning: build failed, waiting for other jobs to finish..

According to added instruction. This command

RUSTFLAGS='-L /usr/lib64' cargo r --example simple

works.