Simplify docs for custom_processing

Author: dannyadair

docs/custom_processing.md

@@ -10,86 +10,22 @@ customize the document generation process. This allows you to:
 
 ## Basic Structure
 
-Your `bake.py` should define a `process_document` function:
+As a naming convention, your `bake.py` needs to define a `process_document` function:
 
 ```python
 from pdfbaker.document import PDFBakerDocument
 
 def process_document(document: PDFBakerDocument) -> None:
     # Custom processing logic here
-    pass
+    return document.process()
 ```
 
-## Document Object
+You will usually just manipulate the data for your templates, and then call `.process()`
+on the document to continue with the built-in stages of combining pages and compressing
+the PDF as configured.
 
-The `document` parameter provides access to:
+See `examples/custom_processing/bake.py` for a simple example of how to do this.
 
-- Document configuration
-- Variant processing
-- Page rendering
-- File management
-
-### Key Methods and Properties
-
-```python
-# Access configuration
-config = document.config
-
-# Process variants
-for variant in document.config.get('variants', []):
-    # Process variant...
-
-# Process pages
-for page in document.config.get('pages', []):
-    # Process page...
-
-# File management
-build_dir = document.build_dir
-dist_dir = document.dist_dir
-```
-
-## Example: Dynamic Pricing
-
-Here's an example that calculates dynamic pricing based on features:
-
-```python
-def process_document(document):
-    # Load pricing data
-    with open('content/pricing_data.yaml') as f:
-        pricing_data = yaml.safe_load(f)
-
-    # Calculate pricing for each variant
-    for variant in document.config.get('variants', []):
-        base_price = document.config['content']['base_price']
-        features = len(variant['content']['features'])
-
-        # Adjust price based on features
-        adjusted_price = base_price * (1 + (features - 1) * 0.1)
-        final_price = adjusted_price * (1 - variant['content']['discount'])
-
-        # Update variant content
-        variant['content']['final_price'] = round(final_price, 2)
-
-    # Process as usual
-    document.process()
-```
-
-## Example: Content Generation
-
-Generate content dynamically based on external data:
-
-```python
-def process_document(document):
-    # Fetch data from API
-    response = requests.get('https://api.example.com/data')
-    data = response.json()
-
-    # Update document content
-    document.config['content'].update({
-        'latest_data': data,
-        'generated_at': datetime.now().isoformat()
-    })
-
-    # Process as usual
-    document.process()
-```
+If you need to fully customise the processing, make sure that your function returns a
+list of Path objects (the PDF files that were created) as that is the expected type of
+return value for logging.