docs: document the e2e package harness

README.md

@@ -231,6 +231,23 @@ Exit codes: 0 all tests passed (skips and flaky allowed), 1 at least one
 test failed (or a `--fail-on` trigger), 2 runtime errors (no declared
 tests, no usable testbed, ...).
 
+## End-to-end package harness
+
+`tests/e2e/` exercises pkh the way it is used in anger: a catalog of ~60
+real source packages (from `hello` and `micro` to `dracut`, `grub2` and
+the kernel) run through the full `pull` → `chlog --rebuild` → `build` →
+`deb` workflow, each stage timed, logged and checked for artifacts:
+
+```
+tests/e2e/run.py --list            # what would run
+tests/e2e/run.py                   # smoke + standard tiers
+tests/e2e/run.py --tier long       # the multi-hour builds
+```
+
+See [tests/e2e/README.md](tests/e2e/README.md) for prerequisites,
+filters (`--only`, `--category`, `--tag`), resume support and the run
+output layout.
+
 ## Future improvement ideas
 
 - pull: try to fetch the correct git branch for series on Debian