Apply suggestions from code review

Co-authored-by: Zyad Hassan <[email protected]>

doc/src/challenges/0013-cstr.md

@@ -23,14 +23,14 @@ a security risk for their users.
 
 ## Description
 
-The goal of this challenge is to ensure the safety of the CStr struct implementation.
+The goal of this challenge is to ensure the safety of the `CStr` struct implementation.
 First, we need to specify a safety invariant that captures the essential safety properties that must be maintained.
 
 Next, we should verify that all the safe, public methods respect this invariant.
 For example, we can check that creating a `CStr` from a byte slice with method `from_bytes_with_nul` will only yield
 safe values of `CStr`.
 
-Finally, for unsafe methods like `as_ptr()` and `from_ptr()`, we need to specify appropriate safety contracts.
+Finally, for unsafe methods like `from_ptr()` and `from_bytes_with_nul_unchecked`, we need to specify appropriate safety contracts.
 These contracts should ensure no undefined behavior occurs within the unsafe methods themselves,
 and that they maintain the overall safety invariant of `CStr` when called correctly.