Clarify that non-artifact-producing modules need `publish / skip := t…

…rue`

We missed this in guardian/permissions#203 - adding
a new subproject that _didn't_ produce a Maven artifact, `sbt-version-policy`
needs to be told to ignore the subproject when performing the automated
compatibility assessment, otherwise it will attempt to download the prior
version of that subproject (which definitely doesn't exist).

See also:

* guardian/permissions#233

docs/configuration.md

@@ -93,7 +93,7 @@ library.
   `1.4.7` release. The workflow will automatically update the `version` during each release, as appropriate.
 
 [Example `build.sbt`](https://github.com/guardian/etag-caching/blob/main/build.sbt)
-* Artifact-producing modules
+* **Artifact-producing modules** - any module (project or subproject) that creates an artifact for Maven Central
   * `organization` - this dictates the [groupId](https://maven.apache.org/guides/mini/guide-naming-conventions.html) of
     your artifacts, and can be either the same as your Sonatype account profile name (eg `com.gu` for the Guardian),
     or a dot-suffixed version of it (eg `com.gu.foobar`) if your project ('foobar') releases multiple artifacts
@@ -108,13 +108,14 @@ library.
     but while this can be a relatively new version of Java, in order for your compiled code to support
     _older_ versions of Java, and avoid `UnsupportedClassVersionError` errors, you'll
     need to set this flag. See also [Scala/Java compatibility](https://docs.scala-lang.org/overviews/jdk-compatibility/overview.html).
-* Top-level 'release' module - if your project has a [multi-module](https://www.scala-sbt.org/1.x/docs/Multi-Project.html)
+* **Non-artifact-producing modules** - any module that _doesn't_ make an artifact to publish to Maven Central
+  (often, the 'root' project in a multi-project build)
+  * `publish / skip := true` (rather than other legacy hacks like `publishArtifact := false`). This setting is
+     respected by `sbt-version-policy` - it won't attempt to calculate compatibility on a module that doesn't
+    publish artifacts.
+* **Top-level 'release' module** - if your project has a [multi-module](https://www.scala-sbt.org/1.x/docs/Multi-Project.html)
   build this could be called 'root', or, if your project only has one module, it and your
   artifact-producing module could be the same thing, and just use top-level settings.
-  * `publish / skip := true` (rather than other legacy hacks like `publishArtifact := false`) for
-    sbt modules that don't generate artifacts (often, the 'root' project in a multi-project build). This
-    setting is respected by `sbt-version-policy` - it won't attempt to calculate compatibility on a module
-    that doesn't publish artifacts.
   * In `releaseProcess`, you'll want _fewer_ steps than
     [the old list specified by `sbt-sonatype`](https://github.com/xerial/sbt-sonatype?tab=readme-ov-file#using-with-sbt-release-plugin),
     now just: