Add Tenstorrent Blackhole tt-nn port

SERVING.md

@@ -38,6 +38,11 @@ tt-model push    build/superpoint-blackhole --publish
 Step 5's `--publish` implies `--public` and adds the `tt-model-catalog` tag, which is what
 lists it in the community catalog.
 
+> **Run every `tt-model` command from this repo's root.** `source.extra_code[].root: code`
+> is resolved against the **current working directory**, not against the YAML's location --
+> verified: loading the same manifest from a parent directory fails with
+> `source.extra_code lists 1 path(s) that do not exist under code`. `cd` into the repo first.
+
 ## What the bundle push does to this repo
 
 - **`code/` and `image/` are replaced wholesale** (`_prune_removed` in `tt_kernel/hub.py`).