README: Better document summarize.py

README.md

@@ -159,10 +159,11 @@ This will build the set of packages defined by the `testedPackages` list in
 After building `testedPackages` (allowing for failures) the CI job runs
 `scripts/summarize.py`, which produces a few artifacts:
 
- * a JSON summary, which includes the full dependency graph as well as which
-   package builds failed
- * a DOT graph showing the package depedencies and their build success
- * a directory of build logs
+ * a JSON summary (`summary.json`) which includes the full dependency graph as
+   well as which package builds failed
+ * a DOT graph (`summary.dot`) showing the package depedencies and their build
+   success. This can be rendered with `scripts/render-graph.sh`.
+ * a directory (`./logs`) of build logs
 
 You can run `scripts/summarize.py` locally with
 ```