Merge pull request #657 from skade/more-enthusiasm

Greet newcomers more enthusiastically

second-edition/src/ch01-02-hello-world.md

@@ -64,7 +64,7 @@ Hello, world!
 On Windows, run `.\main.exe` instead of `./main`. Regardless of your
 operating system, you should see the string `Hello, world!` print to the
 terminal. If you did, then congratulations! You've officially written a Rust
-program. That makes you a Rust programmer! Welcome.
+program. That makes you a Rust programmer! Welcome!
 
 ### Anatomy of a Rust Program