Added filename to top of .rs files

error_handling/errors2.rs

@@ -1,3 +1,4 @@
+// errors2.rs
 // Say we're writing a game where you can buy items with tokens. All items cost
 // 5 tokens, and whenever you purchase items there is a processing fee of 1
 // token. A player of the game will type in how many items they want to buy,