Add a note mentioning that semicolons exist (#2660)

Author: randomPoison

src/types-and-values/hello-world.md

@@ -16,8 +16,9 @@ fn main() {
 What you see:
 
 - Functions are introduced with `fn`.
-- Blocks are delimited by curly braces like in C and C++.
 - The `main` function is the entry point of the program.
+- Blocks are delimited by curly braces like in C and C++.
+- Statements end with `;`.
 - Rust has hygienic macros, `println!` is an example of this.
 - Rust strings are UTF-8 encoded and can contain any Unicode character.