Add cliffhanger about suggestions

Author: blyxyas

book/src/development/writing_tests.md

@@ -202,6 +202,9 @@ The `// run-rustfix` comment will additionally run [rustfix] for our test.
 Rustfix will apply the suggestions from the lint to the test file code and
 compare that to the contents of a `.fixed` file.
 
+We'll talk about suggestions more in depth in a later chapter.
+<!-- FIXME: (blyyas) Link to "Emitting lints" when that gets merged -->
+
 Use `cargo dev bless` to automatically generate the `.fixed` file after running the tests.
 
 [rustfix]: https://github.com/rust-lang/rustfix