first contribution: warn about unsolicited PRs for linter warnings

Linters find issues like usage of deprecated APIs which the project doesn't
want to get fixed because of the work involved and the code churn. New
contributors must be made aware of that because at first glance it looks like
an easy first contribution.

Author: pohly

contributors/guide/first-contribution.md

@@ -20,7 +20,7 @@ description: |
 ## Find something to work on
 
 The first step to getting starting contributing to Kubernetes is to find something
-to work on. Help is always welcome, and no contribution is too small! 
+to work on. Help is always welcome, and no contribution is too small (but see below)!
 
 Here are some things you can do today to get started contributing:
 
@@ -34,6 +34,14 @@ If the above suggestions don't appeal to you, you can browse the
 in contributing without writing code can also find ideas in the 
 [Non-Code Contributions Guide].
 
+{{< note >}}
+Although contributions are welcome, beware that every pull
+request creates work for maintainers and costs for testing it.
+Fixing *linter warnings* is often *not* worth it because the
+existing code is fine. Always discuss with maintainers first
+before creating such PRs.
+{{< /note >}}
+
 ### Find a good first topic
 
 There are [multiple repositories] within the Kubernetes organization.