Docs tweaks

Cargo.toml

@@ -11,6 +11,7 @@ documentation = "https://github.com/kevinmehall/rust-peg/blob/master/README.md#r
 description = "A simple Parsing Expression Grammar (PEG) parser generator."
 keywords = ["peg", "parser", "parsing", "grammar"]
 categories = ["parsing"]
+readme = "README.md"
 
 [dependencies]
 quote = "0.3"

README.md

@@ -127,13 +127,16 @@ the input string parameter, and they are available by name in all action code bl
 
 For an example see [the test](peg-syntax-ext/tests/grammar_args.rs).
 
-Be careful with mutable arguments. Remember that rule actions can run on parse paths that later fail and do not contribute to the final parse.
+The arguments will be passed to each internal parse function, so they must be `Copy` or be a `&`
+or `&mut` reference. Be careful with mutable arguments. Remember that rule actions can run on parse
+paths that later fail and do not contribute to the final parse.
 
 ## Usage
 
 ### With a build script
 
-A Cargo build script can compile your PEG grammar to Rust source automatically.
+A Cargo build script can compile your PEG grammar to Rust source automatically. This method works
+on stable Rust.
 
 [Example crate using rust-peg with a build script](peg-tests/)
 

src/bin.rs

@@ -31,6 +31,7 @@ fn main() {
 			write!(&mut out, "{}", parser).unwrap();
 		}
 		Err(err) => {
+			writeln!(log, "Error compiling rust-peg grammar:").unwrap();
 			writeln!(log, "{}", err).unwrap();
 			process::exit(1);
 		}