Auto update lint count in Clippy book

Author: flip1995

clippy_dev/src/update_lints.rs

@@ -58,6 +58,16 @@ fn generate_lint_files(
         },
     );
 
+    replace_region_in_file(
+        update_mode,
+        Path::new("book/src/README.md"),
+        "[There are over ",
+        " lints included in this crate!]",
+        |res| {
+            write!(res, "{}", round_to_fifty(usable_lints.len())).unwrap();
+        },
+    );
+
     replace_region_in_file(
         update_mode,
         Path::new("CHANGELOG.md"),