chore(docs/maven): document how to specify project homepage in pom.xml (

#22889)

lib/modules/datasource/maven/readme.md

@@ -16,3 +16,14 @@ This is what allows `Renovate` to determine the `sourceUrl`, that it then uses t
 !!! note
     This also works for private repositories.
     It can leverage the same `token` that you had to configure in order to be able to reach the private Artifactory.
+
+#### Specifying your project homepage
+
+When opening a Pull Request `Renovate` uses the top level `url` property to determine the homepage of your project and shows it inside the Pull Request.
+To customize you can set it inside your `pom.xml`.
+
+For example:
+
+```xml
+<url>https://project.example.com</url>
+```