update readme

README.md

@@ -1,9 +1,56 @@
 # exit
 
-This crate exposes a type, `Exit`, which allows using `?` in `main` while also specifying custom exit status codes. See the examples for details. 
+This crate exposes a type, `Exit`, which allows using `?` in `main` while also specifying custom exit status codes. 
 
 The goal of this crate was to provide a proof of concept and sample implementation for the ideas discussed in [this blog post](https://www.joshmcguigan.com/blog/custom-exit-status-codes-rust/). 
 
+## Example
+
+```rust
+#![feature(try_trait)]
+use exit::Exit;
+
+use std::env;
+use std::option;
+
+#[derive(Debug)]
+enum MyErr {
+    MissingArg,
+    ParseErrorUserNum,
+    ParseErrorGroupNum,
+}
+
+impl From<MyErr> for i32 {
+    fn from(err: MyErr) -> Self {
+        match err {
+            MyErr::MissingArg => 2,
+            MyErr::ParseErrorUserNum => 3,
+            MyErr::ParseErrorGroupNum => 4,
+        }
+    }
+}
+
+impl From<option::NoneError> for MyErr {
+    fn from(_: option::NoneError) -> Self {
+        MyErr::MissingArg
+    }
+}
+
+fn main() -> Exit<MyErr> {
+    let user_num_string : String = env::args().skip(1).next()?;
+    let group_num_string : String = env::args().skip(2).next()?;
+
+    let user_num : u32 = user_num_string.parse()
+        .map_err(|_| MyErr::ParseErrorUserNum)?;
+    let group_num : u32 = group_num_string.parse()
+        .map_err(|_| MyErr::ParseErrorGroupNum)?;
+
+    println!("Hello, user #{} from group #{}!", user_num, group_num);
+
+    Exit::Ok
+}
+```
+
 ## License
 
 Licensed under either of

examples/map_err.rs

@@ -2,7 +2,7 @@
 use exit::Exit;
 
 use std::env;
-use core::option;
+use std::option;
 
 #[derive(Debug)]
 enum MyErr {