Provide information about default.toml

README.md

@@ -5,7 +5,9 @@ A tool for formatting Rust code according to style guidelines.
 
 ## How to use
 
-You'll need a pretty up to date version of the **nightly** version of Rust.
+You'll need a pretty up to date version of the **nightly** version of Rust. 
+You will need a default.toml file in the current working directory when you run
+the rustfmt command. You can look at this repo for an example default.toml file.
 
 `cargo build` to build.
 
@@ -201,8 +203,7 @@ It would be really useful to have people use rustfmt on their projects and file
 issues where it does something you don't expect.
 
 A really useful thing to do that on a crate from the Rust repo. If it does
-something unexpected, file an issue; if not, make a PR to the Rust repo with the
-reformatted code. I hope to get the whole repo consistently rustfmt'ed and to
+something unexpected, file an issue; if not, make a PR to the Rust repo with the reformatted code. I hope to get the whole repo consistently rustfmt'ed and to
 replace `make tidy` with rustfmt as a medium-term goal.
 
 ### Create test cases

src/bin/rustfmt.rs

@@ -19,7 +19,9 @@
 
 fn main() {
     let args: Vec<_> = std::env::args().collect();
-    let mut def_config_file = File::open("default.toml").unwrap();
+    let mut def_config_file = File::open("default.toml").unwrap_or_else(|e| {
+        panic!("Unable to open configuration file [default.toml] {}",e)
+    });
     let mut def_config = String::new();
     def_config_file.read_to_string(&mut def_config).unwrap();