new package: Update example to subject: verb version

With the monorepo, we use the `worklog.py` script and the GH UI, which
shows shortlog at a glance.

Therefore, the shortlog messages should be as informative as possible, so
people don't have to go chasing the individual commit logs for relevant
version information when looking for specific updates or summarising the
weekly development churn in the forum sync notes.

This commit changes the old (and no longer useful) "Initial inclusion"
message to a more useful "packagename: Add at version" shortlog message.

Note that we already require "packagename: Update to version" for the
same reason.

Signed-off-by: Rune Morling <ermo@serpentos.com>

docs/packaging/creating-a-new-package.md

@@ -174,7 +174,7 @@ There should be a summary line (with the package name), a blank line, and then t
 Here is an example in our standard format (make sure to check the box in the checklist):
 
 ```
-tree: initial inclusion in the repository
+tree: Add at v2.1.1
 
 **Summary**