chore(project): add code of conduct and commit example (#5255)

commit-example.md

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+# Why this chapter exists
+
+A good commit message enables us:
+
+1. To understand what the contributor is trying to do
+2. Automatically generates change log
+
+## Rule for writing commit message
+
+```md
+# (If applied, this commit will...) <subject> (Max 72 characters)
+
+# |<---- Using a Maximum Of 72 Characters ---->|
+
+# Explain why this change is being made
+
+# |<---- Try To Limit Each Line to a Maximum Of 72 Characters ---->|
+
+# Provide links or keys to any relevant tickets, articles or other resources
+
+# Use issues and merge requests' full URLs instead of short references,
+
+# as they are displayed as plain text outside of GitLab
+
+# --- COMMIT END ---
+
+# --------------------
+
+# Remember to
+
+# Capitalize the subject line
+
+# Use the imperative mood in the subject line
+
+# Do not end the subject line with a period
+
+# Subject must contain at least 3 words
+
+# Separate subject from body with a blank line
+
+# Commits that change 30 or more lines across at least 3 files should
+
+# describe these changes in the commit body
+
+# Do not use Emojis
+
+# Use the body to explain what and why vs. how
+
+# Can use multiple lines with "-" for bullet points in body
+
+# For more information: https://chris.beams.io/posts/git-commit/
+
+# --------------------
+```
+
+## Template for commit messages
+
+Below is a template commit message for your reference.
+
+```md
+feat(components): [el-button] I did something with button
+
+Blank between subject and body is expected.(period is expected)
+Describes your change in one line or multi-line.
+Capitalize your first letter when starting a new line
+Please do not exceeds 72 characters per line, because that would be harder to comprehend.
+
+- You can also add bullet list symbol for better layout
+```
+
+For the subject header, the format is:
+
+```md
+[type](scope): [messages]
+```
+
+You can checkout the allowed values for **type** and **scope** in [commitlint.config.js](https://github.com/element-plus/element-plus/blob/c2ee36a7fc72b17742d43ecdff4e2912c416141d/commitlint.config.js#L57),