Merge pull request #2232 from yegeunyang/#2114

Add a link to declare_lint! macro doc in diagnostics.md

Author: jieyouxu

src/diagnostics.md

@@ -602,7 +602,7 @@ as the linter walks the AST. You can then choose to emit lints in a
 very similar way to compile errors.
 
 You also declare the metadata of a particular lint via the `declare_lint!`
-macro. This includes the name, the default level, a short description, and some
+macro. [This macro](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint_defs/macro.declare_lint.html) includes the name, the default level, a short description, and some
 more details.
 
 Note that the lint and the lint pass must be registered with the compiler.