Add comment by the bot how to launch BCI tests on the staging project

src/staging/bot.py

@@ -1044,6 +1044,18 @@ async def fetch_build_results(self) -> list[RepositoryBuildResult]:
             (await self._run_cmd(self._osc_fetch_results_cmd())).stdout
         )
 
+    @property
+    def staging_project_registry_base_url(self) -> str:
+        """Returns the base url to the containers in the staging project on
+        OBS. This url is missing the repository name and the actual container
+        tag, but it can be used to plug the staging project directly into
+        BCI-tests.
+
+        """
+        return "registry.opensuse.org/" + self.staging_project_name.lower().replace(
+            ":", "/"
+        )
+
     async def force_rebuild(self) -> str:
         """Deletes all binaries of the project on OBS and force rebuilds everything."""
         await self._run_cmd(
@@ -1688,7 +1700,15 @@ async def _create_staging_proj():
         elif action == "query_build_result":
 
             async def print_build_res():
-                return render_as_markdown(await bot.fetch_build_results())
+                prefix = ""
+                # we don't support BCI tests for Tumbleweed yet…
+                if bot.os_version != OsVersion.TUMBLEWEED:
+                    prefix = f"""You can run the BCI test suite against this PR via:
+```ShellSession
+$ OS_VERSION=15.{bot.os_version} TARGET=custom BASEURL={bot.staging_project_registry_base_url} tox -e $ENV -- -n auto
+```
+                """
+                return prefix + render_as_markdown(await bot.fetch_build_results())
 
             coro = print_build_res()