docs(contributing): Add more information for contributors (#60)

Make it easy to understand how to contribute.

.github/CONTRIBUTING.md

@@ -9,8 +9,34 @@ I would recommend reading this guideline for a better development experience.
 
 <br />
 
-- [🔠 Branch Prefix](#-branch-prefix)
 - [🧪 Testing Advice](#-testing-advice)
+- [💬 Commit Message](#-commit-message)
+- [🔠 Branch Prefix](#-branch-prefix)
+- [❓ Pull Requests Title](#-pull-requests-title)
+- [🪵 Commit Log](#-commit-log)
+
+<br /><br />
+
+## 🧪 Testing Advice
+
+There is a test function called [`Test_OAScript`](../lib/oascript_test.go)
+for AppleScript commands.<br />
+When you run this test, your Login Items all will be removed.
+Therefore, I highly recommend backing up your current Login Items by `mli save`.
+
+<br />
+
+## 💬 Commit Message
+
+I recommend you to follow [Conventional Commits] with this format.
+
+```commit message
+type(scope): Description
+
+Body
+```
+
+[Conventional Commits]: https://www.conventionalcommits.org
 
 <br />
 
@@ -38,9 +64,17 @@ For the details of each label, please see [Labels](https://github.com/5ouma/mli/
 
 > Labels were generated with [@azu / github-label-setup](https://github.com/azu/github-label-setup)
 
-## 🧪 Testing Advice
+<br />
 
-There is a test function called [`Test_OAScript`](../lib/oascript_test.go)
-for AppleScript commands.<br />
-When you run this test, your Login Items all will be removed.
-Therefore, I highly recommend backing up your current Login Items by `mli save`.
+## ❓ Pull Requests Title
+
+You don't need to add any prefixes like `feature` or `bug fix`
+to the Pull Requests title because I can recognize what kind of PR it is from labels.
+Please give a clear title.
+
+<br />
+
+## 🪵 Commit Log
+
+I do squash merge to the main branch to keep the commit history clean.
+When merging your Pull Request, I'll add the Conventional Commits type and scope.