docs: add an overview of contribution guidelines

docs/contributing/index.md

@@ -1,15 +1,68 @@
 # Contributing
 
-!!! warning
+This page explains how to contribute to Autoware.
 
-    Under Construction
+First, conform to the [Code of conduct](#contribution-workflows) section for the general manners in contributions.
+
+See the [Contribution workflows](#contribution-workflows) section for the workflows.  
+Also, make sure the contribution is in line with the following guidelines:
+
+- [Coding guidelines](coding-guidelines/index.md): for contributing source code
+- [Testing guidelines](testing-guidelines/index.md): for contributing tests
+- [Documentation guidelines](documentation-guidelines/index.md): for contributing documents
+- [Pull request guidelines](pull-request-guidelines/index.md): for submitting pull requests
+- [Discussion guidelines](discussion-guidelines/index.md): for discussing with other contributors
+- [Support guidelines](../help/support-guidelines.md): for finding the right channel when you need help
+
+It is recommended to read the [Contributing pages in ROS 2 Docs](https://docs.ros.org/en/rolling/Contributing.html) as well because Autoware's guidelines generally depend on them.
+
+For general information about OSS contributions, [Open Source Guides](https://opensource.guide/) by GitHub is a good resource.
+
+!!!info
+
+    If you want to make changes to the guidelines in this documentation site, you can open a new discussion thread and propose it.
+
+## Code of conduct
+
+We welcome contributions from everyone.  
+To ensure our community stays open and healthy, we adhere to the [Contributor Covenant](https://www.contributor-covenant.org/), a widely used [code of conduct](https://github.com/autowarefoundation/autoware/blob/main/CODE_OF_CONDUCT.md) adopted by many other communities listed [here](https://www.contributor-covenant.org/adopters/).
+
+Everyone participating in the Autoware community is expected to follow the code of conduct.  
+If someone in the community happens to be violating these terms, let the maintainers know, and we will address it as soon as possible.
+
+!!!warning
+
+    Note that contributions that ignore guidelines are not contributions but nuisances.
 
 ## Contribution workflows
 
-### Issues
+There are several types of contributions and the workflows differ between the types.
+See the description for your contribution type.
 
 ### Discussions
 
-### Small pull requests
+You can contribute to Autoware by facilitating discussions:
+
+- Find a bug and open a new issue.
+- Propose an idea of features that will enhance Autoware.
+- Join an existing discussion and express your opinion.
+- Organize discussions for other contributors.
+- Answer questions and support other contributors.
+
+See our [support guidelines](../help/support-guidelines.md) for the detailed steps.
+
+### Pull requests
+
+You can submit a pull request directly (without opening an issue) if it is small like the following:
+
+- Update a small part of documents.
+- Fix spelling mistakes.
+- Fix CI failures.
+- Fix warnings detected by compilers or analysis tools.
+- Make small changes to a single package.
+
+Otherwise, create an issue or a discussion thread before submitting a pull request and discuss the approach with maintainers.
+
+Also, regardless of the size of your pull request, follow the pull request template of the target repository.
 
-### Large pull requests
+See our [pull request guidelines](pull-request-guidelines/index.md) for the detailed steps.