docs: updated prefix comments as per requests at end of README.md in Section "Completion", i.e. I added some hopefully useful text to errors4.rs and 5 and option1.rs 2 and 3. Just attempt to do something useful for repository as first commit.

exercises/error_handling/errors4.rs

@@ -1,4 +1,6 @@
 // errors4.rs
+// The code is excessively positive about the numbers given it. It should fail if
+// they aren't, returning the appropriate Result.
 // Make this test pass! Execute `rustlings hint errors4` for hints :)
 
 // I AM NOT DONE

exercises/error_handling/errors5.rs

@@ -1,7 +1,8 @@
 // errors5.rs
 
 // This program uses a completed version of the code from errors4.
-// It won't compile right now! Why?
+// It won't compile right now! Why? What are all the possible return
+// types from main?
 // Execute `rustlings hint errors5` for hints!
 
 // I AM NOT DONE

exercises/option/option1.rs

@@ -1,4 +1,6 @@
 // option1.rs
+// How does the function signature of print_number differ from where
+// it is called in main?
 // Make me compile! Execute `rustlings hint option1` for hints
 
 // I AM NOT DONE

exercises/option/option2.rs

@@ -1,4 +1,8 @@
 // option2.rs
+// You're gonna add if let and while let to the function below
+// where the todo: are
+// what's the difference between 'word' and 'optional_word'
+// and how do you get one from the other?
 // Make me compile! Execute `rustlings hint option2` for hints
 
 // I AM NOT DONE

exercises/option/option3.rs

@@ -1,4 +1,5 @@
 // option3.rs
+// Let the compiler guide you. Also: https://doc.rust-lang.org/std/keyword.ref.html
 // Make me compile! Execute `rustlings hint option3` for hints
 
 // I AM NOT DONE