Add readme with basic example

Readme.md

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+Cursive
+=======
+
+Cursive is a ncurses-based TUI (Text User Interface) library for rust. It is based on jeaye's [ncurses-rs](https://github.com/jeaye/ncurses-rs).
+
+It is designed to be safe, and easy to use:
+
+```rust
+extern crate cursive;
+
+use cursive::{Cursive,Dialog};
+
+fn main() {
+	let mut siv = Cursive::new();
+
+	// Create a popup window with a "Ok" button that quits the application
+	siv.add_layer(Dialog::new("Hello world!").button("Ok", |s| s.quit()));
+
+	// Starts the event loop.
+	siv.run();
+}
+```