doc: add guide to submit PR (#665)

Signed-off-by: spacewander <spacewanderlzx@gmail.com>

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,37 @@
+<!--
+Please change the [issue] below to the number of issue which is addressed by this
+pull request if there is one.
+If the pull request references an issue X but does not close it, please change the
+prompt to "Ref #X".
+If there is no issue, please remove this prompt.
+-->
+
+Fix #[issue]
+
+<!--
+Before submitting a pull request, please make sure the following is done:
+* If your change is a bugfix, please add tests which can reproduce the bug.
+* If your change is a new feature, please add tests which cover the new functionality, and
+update the doc under `site/content/`. You can update one of the doc written in your familiar language.
+It's appreciated if you can update both the English and Chinese doc if you know both languages.
+
+If you want to add an E2E test, please add it in `e2e/tests/`.
+If you want to add an integration test, please add it in (depending which module you are working on):
+* ./api/tests/integration
+* ./plugins/tests/integration
+* ./controller/tests/integration
+
+You can run the test in the CI by enabling GitHub Action in your own fork and submitting a pull request
+to your own fork. Alternatively, you can run the test locally by following the instructions in the CI configuration.
+
+Feel free to ask for help if you need.
+
+If your pull request is still in progress, you can submit a draft PR:
+https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-stage-of-a-pull-request.
+
+Once your pull request is ready for review, please don't use `push -f` which will break the review progress.
+Please use `merge main` to resolve merge conflicts, instead of `rebase main`.
+Please use "request review" to notify the reviewer after making changes:
+https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/requesting-a-pull-request-review.
+Or you can @ the reviewer in the comment to notify the reviewer.
+-->