PRs: document policy around linter checks

Occasionally contributors run linters, fix issues found by them (sometimes
automatically!) and then create PRs. This creates work for maintainers and is
often not useful, so let's write this down. Perhaps future contributors will
find it, if not, we can point to it in PRs when closing them.

Author: pohly

contributors/guide/pull-requests.md

@@ -590,6 +590,58 @@ at once to that file.
 * Can the file be improved further?
 * Does the trivial edit greatly improve the quality of the content?
 
+## Fixing linter issues
+
+Kubernetes has a set of linter checks. Some of those must pass in the entire
+code base, some must pass in new or modified code, and some are merely hints
+to developers how to improve their code.
+
+Please do not create Pull Requests for issues found by linters without first
+reaching out to maintainers on the `#code-organization`
+[Slack](http://slack.kubernetes.io) channel to determine whether there is
+sufficient interest in fixing such issues.
+
+When it was discussed, make sure to include people who gave the preliminary
+approval of this work as well as the link to the discussion on Slack or GitHub
+issue into the PR description. This is a good example to follow:
+
+> /area code-organization
+>
+> This PR fixes linter rules discussed in the Slack https://kubernetes.slack.com/archives/Foo/Bar.
+> Preliminary agreement to address those issues were given by @GHHandle1 and @GHHandle2.
+>
+> /assign @GHHandle1
+> /assign @GHHandle2
+>
+> This PR fixes issues in the package:
+> pkg/kubelet
+>
+> Related PRs for other packages:
+> - github.com/link-to-other-PR1
+> - github.com/link-to-other-PR2
+
+It does not matter whether the linter is enabled in Kubernetes or not:
+- If a linter *is* enabled in
+  [golangci.yaml](https://github.com/kubernetes/kubernetes/blob/master/hack/golangci.yaml),
+  then it has already been determined that sweeping changes in the existing
+  code aren't necessary or just are not worth the cost (e.g. causing rebases of other
+  Pull Requests or obscuring authorship).
+- If a linter *is not* enabled, then it might not be important enough.
+- If the check is performed by third party tools which are not integrated in
+  the Kubernetes CI or proprietary, file a bug or start a discussion about it first.
+
+Such Pull Requests are often large and thus hard to review. When the linter
+enforces some opinion or policy, then this is not necessarily something that
+applies to Kubernetes. Kubernetes uses the formatting rules enforced by Go.
+Stricter rules like specific usage of
+[whitespace](https://golangci-lint.run/usage/linters/#whitespace) or using
+[standard library constants](https://golangci-lint.run/usage/linters/#usestdlibvars)
+are opinionated and not worth the cost of introducing them now.
+
+Linters worth considering are those which actually improve code correctness,
+for example by warning about suspicious code like calling a function and then
+not checking the error result.
+
 # The Testing and Merge Workflow
 
 The Kubernetes merge workflow uses labels, applied by [commands](https://prow.k8s.io/command-help) via comments.