Update README.md (dart-lang/lints#27)

Update README.md

pkgs/lints/README.md

diff --git a/pkgs/lints/README.md b/pkgs/lints/README.md
index 243e050..7e0305c 100644
--- a/pkgs/lints/README.md
+++ b/pkgs/lints/README.md
@@ -52,6 +52,12 @@
 include: package:lints/recommended.yaml
 ```
 
+or:
+
+```yaml
+include: package:lints/core.yaml
+```
+
 ## Customizing the pre-defined lint sets
 
 You can customize the pre-defined lint sets, both to disable one or more of the