Merge pull request #3889 from rust-lang/chriskrycho/ch-3-break-vs-return

Chapter 3: Clarify `return` vs. `break`.

src/ch03-05-control-flow.md

@@ -250,6 +250,9 @@ and then check whether the `counter` is equal to `10`. When it is, we use the
 semicolon to end the statement that assigns the value to `result`. Finally, we
 print the value in `result`, which in this case is `20`.
 
+You can also `return` from inside a loop. While `break` only exits the current
+loop, `return` always exits the current function.
+
 #### Loop Labels to Disambiguate Between Multiple Loops
 
 If you have loops within loops, `break` and `continue` apply to the innermost