fix: image link in `lib.rs` instead of `readme.md`

src/lib.rs

@@ -162,13 +162,11 @@
 //! \
 //! diagnostic error code: oops::my::bad (link)
 //! Error: oops!
-//!
 //! \
 //! Begin snippet for bad_file.rs starting
 //! at line 2, column 3
 //! \
 //! snippet line 1: source
-//!
 //! \
 //! snippet line 2:  text
 //!     highlight starting at line 1, column 3: This bit here