chore: add pull request template (#569)

Signed-off-by: Ryan Wang <i@ryanc.cc>

.github/pull_request_template.md

@@ -0,0 +1,76 @@
+<!--  Thanks for sending a pull request!  Here are some tips for you:
+1. 如果这是你的第一次，请阅读我们的贡献指南：<https://github.com/halo-dev/halo/blob/master/CONTRIBUTING.md>。
+1. If this is your first time, please read our contributor guidelines: <https://github.com/halo-dev/halo/blob/master/CONTRIBUTING.md>.
+2. 请根据你解决问题的类型为 Pull Request 添加合适的标签。
+2. Please label this pull request according to what type of issue you are addressing, especially if this is a release targeted pull request.
+3. 请确保你已经添加并运行了适当的测试。
+3. Ensure you have added or ran the appropriate tests for your PR.
+-->
+
+#### What type of PR is this?
+
+<!--
+添加其中一个类别：
+Add one of the following kinds:
+
+/kind bug
+/kind cleanup
+/kind documentation
+/kind feature
+/kind optimization
+
+适当添加其中一个或多个类别（可选）：
+Optionally add one or more of the following kinds if applicable:
+
+/kind api-change
+/kind deprecation
+/kind failing-test
+/kind flake
+/kind regression
+-->
+
+#### What this PR does / why we need it:
+
+#### Which issue(s) this PR fixes:
+
+<!--
+PR 合并时自动关闭 issue。
+Automatically closes linked issue when PR is merged.
+
+用法：`Fixes #<issue 号>`，或者 `Fixes (粘贴 issue 完整链接)`
+Usage: `Fixes #<issue number>`, or `Fixes (paste link of issue)`.
+-->
+Fixes #
+
+#### Screenshots:
+
+<!--
+如果此 PR 有 UI 的改动，最好截图说明这个 PR 的改动。
+If there are UI changes to this PR, it is best to take a screenshot to illustrate the changes to this PR.
+
+eg.
+
+Before:
+
+![screenshot-before](https://user-images.githubusercontent.com/screenshot.png)
+
+After:
+
+![screenshot-after](https://user-images.githubusercontent.com/screenshot.png)
+-->
+
+#### Special notes for your reviewer:
+
+#### Does this PR introduce a user-facing change?
+
+<!--
+如果当前 Pull Request 的修改不会造成用户侧的任何变更，在 `release-note` 代码块儿中填写 `NONE`。
+否则请填写用户侧能够理解的 Release Note。如果当前 Pull Request 包含破坏性更新（Break Change），
+Release Note 需要以 `action required` 开头。
+If no, just write "NONE" in the release-note block below.
+If yes, a release note is required:
+Enter your extended release note in the block below. If the PR requires additional action from users switching to the new release, include the string "action required".
+-->
+
+```release-note
+```