doc: contributing.md (#67)

CONTRIBUTING.md

@@ -1,6 +1,35 @@
-# How to Contribute
+# Contributing to GreptimeDB
+
+Much appreciate for your interest in contributing to GreptimeDB! This document list some guidelines for contributing to our code base.
+
+To learn about the design of GreptimeDB, please refer to the [design docs](https://github.com/GrepTimeTeam/docs).
 
 ## Pull Requests
-### Commit Messages
-All commit messages SHOULD adhere to the [Conventional Commits specification](https://conventionalcommits.org/)
 
+### Before PR
+- Make sure all unit tests are passed.
+- Make sure all clippy warnings are fixed (you can check it locally by running `cargo clippy --workspace --all-targets -- -D warnings -D clippy::print_stdout -D clippy::print_stderr`).
+
+### Title
+
+The titles of pull requests should be prefixed with category name listed in [Conventional Commits specification](https://www.conventionalcommits.org/en/v1.0.0) 
+like `feat`/`fix`/`doc`, with a concise summary of code change follows. DO NOT use last commit message as pull request title.
+
+### Description
+
+- If your pull request is small, like a typo fix, feel free to go brief.
+- But if it contains large code change, make sure to state the motivation/design details of this PR so that reviewers can understand what you're trying to do.
+- If the PR contains any breaking change or API change, make sure that is clearly listed in your description.
+
+### Commit Messages
+
+All commit messages SHOULD adhere to the [Conventional Commits specification](https://conventionalcommits.org/).
+
+## Getting help
+
+There are many ways to get help when you're stuck. It is recommended to ask for help by opening an issue, with a detailed description
+of what you were trying to do and what went wrong. You can also reach for help in our Slack channel.
+
+
+## Bug report
+To report a bug or a security issue, you can [open a new GitHub issue](https://github.com/GrepTimeTeam/greptimedb/issues/new).