grumphp: add page (#3570)

pages/common/grumphp.md

@@ -0,0 +1,16 @@
+# grumphp
+
+> A composer plugin that enables source code quality checks.
+> More information: <https://github.com/phpro/grumphp>.
+
+- Register the Git hooks:
+
+`grumphp git:init`
+
+- Trigger the pre-commit hook manually:
+
+`grumphp git:pre-commit`
+
+- Check every versioned file:
+
+`grumphp run`