add contrib memo

Author: woensug-choi

README.md

@@ -3,3 +3,5 @@
 All documentation of Project DAVE can be found in the [Dave Documentation (https://field-robotics-lab.github.io/dave.doc/)](https://field-robotics-lab.github.io/dave.doc/).
 
 The documentation source code is in the [Field-Robotics-Lab/dave.doc](https://github.com/Field-Robotics-Lab/dave.doc) repository.
+
+For contribution, do `pre-commit install` before commit.