docs: a relative output.dir is read from where you run, not from the recipe

Measured on 2026-09-02: a recipe kept in recipes/ with dir: out, run from
somewhere else, writes into out beside the caller rather than beside the
recipe. The behaviour has been the same since the beginning and was written
down nowhere, so the first person keeping recipes in their own directory had
to find it by looking for the files.

The key table now says it, with the way to pin it down.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: donislawdev

README.md

@@ -377,9 +377,12 @@ tfg generate fixtures.yaml
 | `seed` | the number that makes a run repeatable. Same seed, same bytes |
 | `defaults.label` | write the self describing label inside each file. Default `true` |
 | `targets` | the list of things to produce. See below |
-| `output.dir` | where the files and the manifest go |
+| `output.dir` | where the files and the manifest go. A relative path is read from the directory you run in, not from the one the recipe sits in |
 | `output.manifest` | manifest file name. Default `manifest.json` |
 
+So a recipe kept in `recipes/` with `dir: out` writes into `out` next to you, not
+next to the recipe. Give an absolute path, or `--out`, when you want it fixed.
+
 ### Target keys
 
 | key | meaning |