Apply suggestions from code review

Co-authored-by: Daniel McCarney <[email protected]>

CONTRIBUTING.md

@@ -77,18 +77,18 @@ and forth across the FFI boundary.
 
 # Helper macros
 
-We have an API guideline that we always check input pointers for NULL, and
-return an error rather than dereferencing a NULL pointer. To help with that,
-we have a number of helper macros that early-return if a pointer is NULL:
-
- - try_ref_from_ptr!
- - try_mut_from_ptr!
- - try_box_from_ptr!
- - try_clone_arc!
- - try_callback!
- - try_slice!
- - try_take!
-
-These are defined in src/lib.rs. The `Castable` trait determines which
+We have an API guideline that we always check input pointers for `NULL`, and
+return an error rather than dereferencing a `NULL` pointer. To help with that,
+we have a number of helper macros that early-return if a pointer is `NULL`:
+
+ - `try_ref_from_ptr!`
+ - `try_mut_from_ptr!`
+ - `try_box_from_ptr!`
+ - `try_clone_arc!`
+ - `try_callback!`
+ - `try_slice!`
+ - `try_take!`
+
+These are defined in [src/lib.rs](src/lib.rs). The `Castable` trait determines which
 C pointers can be cast to which Rust pointer types. These macros rely
 on that trait to ensure correct typing of conversions.