docs: expand README and add architecture/contributing notes

Document resume, dependencies, external tools, dev commands, and MIT license.

Co-authored-by: Cursor <cursoragent@cursor.com>

README.md

@@ -7,15 +7,19 @@ Each pipeline is a Python script that defines a DAG of processing steps. Every s
 ## Requirements
 
 - Python 3.11+
-- [ImageMagick](https://imagemagick.org/) (`magick` or `convert` on PATH)
+- [ImageMagick](https://imagemagick.org/) (`magick` or `convert` on PATH) — most pipelines
+- Optional CLIs per module: [G'MIC](https://gmic.eu/), [rembg](https://github.com/danielgatis/rembg), [darktable-cli](https://www.darktable.org/), GIMP (`gimp-console`)
 
 ## Installation
 
 ```bash
 cd /path/to/imagepipeline
-pip install -e ".[dev]"
+pip install -e ".[dev]"      # core + tests
+pip install -e ".[dev,ai]"   # + torch/numpy for AI modules
 ```
 
+Copy `.env.example` to `.env` and set `OPENROUTER_API_KEY` when using `openrouter_edit` or Comfy-related workflows.
+
 ## Quick Start
 
 Edit the input path in `pipelines/example_grayscale.py`, then run:
@@ -35,9 +39,11 @@ with Pipeline(name="my_run", input_dir=Path("/path/to/export")) as p:
     p.run()
 ```
 
+List registered modules: `imagepipeline list-modules`
+
 ## Output Structure
 
-Each run creates a folder like `my_run_20260527143022/`:
+Each run creates a folder like `my_run_20260527143022/` under `~/pipeline_output/` (or `output_base`):
 
 ```
 my_run_20260527143022/
@@ -50,6 +56,25 @@ my_run_20260527143022/
 
 Step folders are named `{module_name}_{nn}` by default (two-digit counter per module name). Pass optional `step_id="input_bokeh"` to `p.step()` for a custom folder name and step reference (see [docs/MODULE_DEVELOPMENT.md](docs/MODULE_DEVELOPMENT.md#step-folder-naming)).
 
+## Resume
+
+Pipelines support resuming interrupted runs:
+
+```python
+CONTINUE_FROM = Path("~/pipeline_output/my_run_260718120000")
+EXISTING_OUTPUTS = {"rembg_01": CONTINUE_FROM / "rembg_01"}
+
+with Pipeline(
+    name="my_run",
+    input_dir=INPUT,
+    continue_from=CONTINUE_FROM,
+    existing_outputs=EXISTING_OUTPUTS,
+) as p:
+    ...
+```
+
+Modules that change file extensions must implement `expected_output_filenames` so skip logic works (e.g. `rembg` → `.png`).
+
 ## Writing Pipelines
 
 Pipelines are plain Python scripts. Reference previous steps via `StepRef` objects returned by `p.step()`:
@@ -67,12 +92,27 @@ with Pipeline(name="colorsplash", input_dir=INPUT) as p:
 - Parameters are passed as kwargs and validated against each module's schema
 - Multiple uses of the same module get separate numbered folders
 
+Declarative building blocks for agents and humans: [RECIPES.md](RECIPES.md).
+
 ## Adding Modules
 
-See [docs/MODULE_DEVELOPMENT.md](docs/MODULE_DEVELOPMENT.md).
+See [docs/MODULE_DEVELOPMENT.md](docs/MODULE_DEVELOPMENT.md). Architecture overview: [docs/ARCHITECTURE.md](docs/ARCHITECTURE.md).
+
+## Development
+
+```bash
+ruff check .
+ruff format .
+pytest                      # full suite (uses local CLIs when present)
+pytest -m "not integration" # fast subset (CI default)
+```
+
+See [CONTRIBUTING.md](CONTRIBUTING.md).
 
 ## Tests
 
 ```bash
 pytest
 ```
+
+Optional AI tests require `pip install -e ".[ai]"`.