Add CLAUDE.md with comprehensive technical documentation for WellData FHIR IG

Introduced a detailed guide outlining the project structure, build instructions, FHIR profiles, example creation, and documentation setup. Includes instructions on using Docker, SUSHI, and the HL7 FHIR IG Publisher for seamless development and deployment.

Author: rolandgroen

CLAUDE.md

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+# WellData FHIR Implementation Guide
+
+## Project Overview
+
+This is a FHIR R4 Implementation Guide for the WellData project, which enables personal health data storage in Solid pods with FHIR-based access.
+
+## Technology Stack
+
+- **FHIR Shorthand (FSH)**: Profiles and examples defined in `input/fsh/`
+- **SUSHI**: FSH compiler
+- **HL7 FHIR IG Publisher**: Generates the full Implementation Guide
+- **Docker**: Build environment
+
+## Project Structure
+
+```
+├── input/
+│   ├── fsh/
+│   │   ├── profiles/          # FHIR profile definitions (FSH)
+│   │   └── instances/         # Example instances (FSH)
+│   ├── pagecontent/           # Markdown documentation pages
+│   └── images-source/         # PlantUML diagrams
+├── sushi-config.yaml          # SUSHI/IG configuration
+├── ig.ini                     # IG Publisher configuration
+├── Makefile                   # Build targets
+├── Dockerfile                 # Build environment
+└── docker-entrypoint.sh       # Docker entry point
+```
+
+## Build Commands
+
+All builds use Docker. First build the image:
+
+```shell
+docker build . -t gidsopenstandaarden-welldata-ig
+```
+
+Then run targets:
+
+```shell
+# Full IG build (generates HTML, JSON, TTL)
+docker run --rm -v "${PWD}:/src" gidsopenstandaarden-welldata-ig build
+
+# SUSHI only (quick FSH validation)
+docker run --rm -v "${PWD}:/src" gidsopenstandaarden-welldata-ig sushi
+
+# Show available targets
+docker run --rm -v "${PWD}:/src" gidsopenstandaarden-welldata-ig help
+```
+
+## Key Configuration
+
+In `sushi-config.yaml`:
+- `FSHOnly: false` - Generate full IG structure
+- `excludettl: false` - Generate TTL (RDF) output
+- `excludexml: true` - Skip XML output
+
+## FHIR Profiles
+
+| Profile | File | Description |
+|---------|------|-------------|
+| WellDataPatient | `profiles/WellDataPatient.fsh` | Patient demographic data |
+| WellDataObservation | `profiles/WellDataObservation.fsh` | Health observations (vitals, lab results, surveys) |
+| WellDataQuestionnaire | `profiles/WellDataQuestionnaire.fsh` | Questionnaire definitions |
+| WellDataQuestionnaireResponse | `profiles/WellDataQuestionnaireResponse.fsh` | Questionnaire answers |
+
+## Adding Examples
+
+Add FSH instances in `input/fsh/instances/`. Example:
+
+```fsh
+Instance: example-new-observation
+InstanceOf: WellDataObservation
+Title: "New Observation Example"
+* status = #final
+* code.coding.system = "http://snomed.info/sct"
+* code.coding.code = #12345678
+* subject.reference = "Patient/example-welldata-patient"
+* effectiveDateTime = "2025-06-10T09:00:00+02:00"
+* valueQuantity.value = 100
+* valueQuantity.unit = "mg/dL"
+```
+
+## Adding Documentation Pages
+
+1. Create markdown file in `input/pagecontent/`
+2. Add to `pages:` section in `sushi-config.yaml`
+3. Add to `menu:` section in `sushi-config.yaml`
+
+## PlantUML Diagrams
+
+Place `.plantuml` files in `input/images-source/`. Reference in markdown:
+
+```markdown
+{::nomarkdown}
+{% include diagram-name.svg %}
+{:/}
+```
+
+## Output
+
+After `make build`, output is in `output/`:
+- `*.html` - Documentation pages
+- `*.json` - FHIR resources as JSON
+- `*.ttl` - FHIR resources as RDF/Turtle
+- `package.tgz` - FHIR package for distribution
+
+## Git Conventions
+
+- Do not commit `output/`, `fsh-generated/`, `temp/`, `input-cache/`
+- Use `git rm -f` for deletions, `git mv` for moves
+- Add new files to git immediately