- propagate renaming for crate to fastwave_backend

- repair scope printout from example/vcd.rs
 - update and improve instruction for running examples in README

examples/parse_vcd.rs

@@ -5,7 +5,7 @@
 use clap::Parser;
 use std::fs::File;
 
-use fastwave::*;
+use fastwave_backend::*;
 
 use num::{BigUint};