[Enhancement]: Add issue and PR template (#966)

* add issue and PR template

* rephrase

* fix lint

* resolve comments

* fix typo

* resolve comment

.github/ISSUE_TEMPLATE/config.yml

+blank_issues_enabled: false
+
+contact_links:
+  - name: Common Issues
+    url: https://mmcv.readthedocs.io/en/latest/trouble_shooting.html
+    about: Check if your issue already has solutions
+  - name: MMCV Documentation
+    url: https://mmcv.readthedocs.io/en/latest/
+    about: Check if your question is answered in docs

.github/ISSUE_TEMPLATE/feature_request.md

+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Describe the feature**
+
+**Motivation**
+A clear and concise description of the motivation of the feature.
+Ex1. It is inconvenient when [....].
+Ex2. There is a recent paper [....], which is very helpful for [....].
+
+**Related resources**
+If there is an official code release or third-party implementations, please also provide the information here, which would be very helpful.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.
+If you would like to implement the feature and create a PR, please leave a comment here and that would be much appreciated.

.github/ISSUE_TEMPLATE/general_questions.md

+---
+name: General questions
+about: Ask general questions to get help
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Checklist**
+
+1. I have searched related issues but cannot get the expected help.
+2. I have read the FAQ documentation but cannot get the expected help.

.github/ISSUE_TEMPLATE/unexpected_report.md

+---
+name: Unexpected Results
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+Thanks for reporting the unexpected results and we appreciate it a lot.
+
+**Checklist**
+
+1. I have searched related issues but cannot get the expected help.
+2. I have read the [FAQ documentation](https://mmcv.readthedocs.io/en/latest/trouble_shooting.html) but cannot get the expected help.
+3. The unexpected results still exist in the latest version.
+
+**Describe the Issue**
+A clear and concise description of what the bug is, including what results are expected and what the real results you got.
+
+**Reproduction**
+
+1. What command, code, or script did you run?
+
+```bash
+A placeholder for the command.
+```
+
+2. Did you make any modifications on the code? Did you understand what you have modified?
+
+**Environment**
+
+1. Please run `python -c "from mmcv.utils import collect_env; print(collect_env())"` to collect necessary environment information and paste it here.
+2. You may add addition that may be helpful for locating the problem, such as
+    - How you installed PyTorch [e.g., pip, conda, source]
+    - Other environment variables that may be related (such as `$PATH`, `$LD_LIBRARY_PATH`, `$PYTHONPATH`, etc.)
+
+**Error traceback**
+If applicable, paste the error traceback here.
+
+```none
+A placeholder for traceback.
+```
+
+**Bug fix**
+If you have already identified the reason, you can provide the information here. If you are willing to create a PR to fix it, please also leave a comment here and that would be much appreciated!

.github/pull_request_template.md

+Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.
+
+## Motivation
+Please describe the motivation of this PR and the goal you want to achieve through this PR.
+
+## Modification
+Please briefly describe what modification is made in this PR.
+
+## BC-breaking (Optional)
+Does the modification introduce changes that break the back-compatibility of the downstream repos?
+If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.
+
+## Use cases (Optional)
+If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.
+
+## Checklist
+
+1. Pre-commit or other linting tools are used to fix the potential lint issues.
+2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
+3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
+4. The documentation has been modified accordingly, like docstring or example tutorials.

mmcv/ops/csrc/onnxruntime/cpu/roi_align_rotated.cpp

@@ -2,6 +2,7 @@
 // https://github.com/facebookresearch/detectron2/tree/master/detectron2/layers/csrc/ROIAlignRotated
 // Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
 #include "roi_align_rotated.h"
+
 #include "../ort_mmcv_utils.h"
 
 struct PreCalc {