CONTRIBUTING: add instructions about how to run and bless tests

Author: nbdd0121

CONTRIBUTING.md

@@ -1,9 +1,16 @@
 # Contributing
 
+## Testing
+
+Test can be run via `cargo test --release`.
+For UI tests, they can be blessed (updated) with `BLESS=1 cargo test --release`.
+
+## Guidelines
+
 There is currently no specific guidelines for contributing to klint.
 However, you should in general follow the guidelines to contribute to the Linux kernel and the Rust language.
 
-## Generated Contents
+### Generated Contents
 
 There is no ban on using langauge models to assist development, but doing so should follow [generated content guideline](https://www.kernel.org/doc/html/next/process/generated-content.html) in the kernel.
 Pull requests that are fully or mainly generated by AI is not welcome and will be closed in line with [burdensome PR policy](https://github.com/rust-lang/compiler-team/issues/893) of the Rust compiler.