Merge the two CONTRIBUTING.md's (#2543)

- Remove `./.github/CONTRIBUTING.md`, while merging some parts of it
  into the top-level CONTRIBUTING.md.
- Link to the top-level CONTRIBUTING.md from README.md

Signed-off-by: Adrian Preston <PRESTONA@uk.ibm.com>

CONTRIBUTING.md

@@ -1,11 +1,28 @@
-## Contributing
+# Contributing
 
 [fork]: https://github.com/IBM/sarama/fork
 [pr]: https://github.com/IBM/sarama/compare
 [released]: https://help.github.com/articles/github-terms-of-service/#6-contributions-under-repository-license
 
 Hi there! We are thrilled that you would like to contribute to Sarama.
-Your help is essential for keeping it great.
+Contributions are always welcome, both reporting issues and submitting pull requests!
+
+## Reporting issues
+
+Please make sure to include any potentially useful information in the issue, so we can pinpoint the issue faster without going back and forth.
+
+- What SHA of Sarama are you running? If this is not the latest SHA on the main branch, please try if the problem persists with the latest version.
+- You can set `sarama.Logger` to a [log.Logger](http://golang.org/pkg/log/#Logger) instance to capture debug output. Please include it in your issue description.
+- Also look at the logs of the Kafka broker you are connected to. If you see anything out of the ordinary, please include it.
+
+Also, please include the following information about your environment, so we can help you faster:
+
+- What version of Kafka are you using?
+- What version of Go are you using?
+- What are the values of your Producer/Consumer/Client configuration?
+
+
+## Contributing a change
 
 Contributions to this project are [released][released] to the public under the project's [opensource license](LICENSE.md).
 By contributing to this project you agree to the [Developer Certificate of Origin](https://developercertificate.org/) (DCO).
@@ -19,12 +36,26 @@ feat: this is my commit message
 Signed-off-by: Random J Developer <random@developer.example.org>
 ```
 
-Git even has a `-s` command line option to append this automatically to your commit message:
+Git even has a `-s` command line option to append this automatically to your
+commit message:
 
 ```
 $ git commit -s -m 'This is my commit message'
 ```
 
+Because this library is in production use by many people and applications, we code review all additions.
+To make the review process go as smooth as possible, please consider the following.
+
+- If you plan to work on something major, please open an issue to discuss the design first.
+- Don't break backwards compatibility. If you really have to, open an issue to discuss this first.
+- Make sure to use the `go fmt` command to format your code according to the standards. Even better, set up your editor to do this for you when saving.
+- Run [go vet](https://golang.org/cmd/vet/) to detect any suspicious constructs in your code that could be bugs.
+- Explicitly handle all error return values. If you really want to ignore an error value, you can assign it to `_`. You can use [errcheck](https://github.com/kisielk/errcheck) to verify whether you have handled all errors.
+- You may also want to run [golint](https://github.com/golang/lint) as well to detect style problems.
+- Add tests that cover the changes you made. Make sure to run `go test` with the `-race` argument to test for race conditions.
+- Make sure your code is supported by all the Go versions we support.
+  You can rely on GitHub Actions for testing older Go versions.
+
 ## Submitting a pull request
 
 0. [Fork][fork] and clone the repository
@@ -44,3 +75,4 @@ Here are a few things you can do that will increase the likelihood of your pull
 - [How to Contribute to Open Source](https://opensource.guide/how-to-contribute/)
 - [Using Pull Requests](https://help.github.com/articles/about-pull-requests/)
 - [GitHub Help](https://help.github.com)
+

README.md

@@ -25,7 +25,7 @@ A changelog is available [here](CHANGELOG.md).
 
 ## Contributing
 
-- Get started by checking our [contribution guidelines](https://github.com/IBM/sarama/blob/main/.github/CONTRIBUTING.md).
+- Get started by checking our [contribution guidelines](https://github.com/IBM/sarama/blob/main/CONTRIBUTING.md).
 - Read the [Sarama wiki](https://github.com/IBM/sarama/wiki) for more technical and design details.
 - The [Kafka Protocol Specification](https://cwiki.apache.org/confluence/display/KAFKA/A+Guide+To+The+Kafka+Protocol) contains a wealth of useful information.
 - For more general issues, there is [a google group](https://groups.google.com/forum/#!forum/kafka-clients) for Kafka client developers.