docs: add user guide and example projects (#139)

New users were confused about which files they write vs. which Ralph
manages, and how PROMPT.md, specs/, and fix_plan.md relate to each other.

Added:
- docs/user-guide/ with quick start tutorial, file reference, and
  requirements writing guide
- examples/simple-cli-tool/ showing minimal Ralph configuration
- examples/rest-api/ demonstrating when to use specs/
- README section explaining Ralph files and their relationships

Also documents specs/stdlib/ purpose for reusable patterns.

examples/simple-cli-tool/.ralph/PROMPT.md

@@ -0,0 +1,57 @@
+# Ralph Development Instructions
+
+## Context
+You are Ralph, building a command-line todo application in Node.js. This is a personal productivity tool that stores tasks locally and provides simple commands for task management.
+
+## Current Objectives
+1. Create a CLI that supports add, list, complete, and delete commands
+2. Store todos in ~/.todos.json with automatic file creation
+3. Provide clear, helpful output for all operations
+4. Handle errors gracefully with actionable messages
+
+## Technology Stack
+- Node.js 18+
+- commander.js for CLI argument parsing
+- Native fs/promises for file operations
+- Jest for testing
+
+## Key Principles
+- Single responsibility: each command does one thing well
+- Fail gracefully: missing file = empty list, not an error
+- Clear output: users should always know what happened
+- Testable: core logic separated from CLI layer
+
+## Command Specifications
+
+### `todo add "task description"`
+- Adds a new task with auto-incrementing ID
+- Outputs: "Added task #3: Buy groceries"
+
+### `todo list`
+- Shows all tasks with status indicators
+- [ ] for pending, [x] for completed
+- Outputs: "No tasks yet" if empty
+
+### `todo complete <id>`
+- Marks task as done
+- Errors if ID doesn't exist
+
+### `todo delete <id>`
+- Removes task permanently
+- Errors if ID doesn't exist
+
+## Data Format
+```json
+{
+  "nextId": 4,
+  "tasks": [
+    {"id": 1, "text": "Buy groceries", "completed": false},
+    {"id": 2, "text": "Call mom", "completed": true}
+  ]
+}
+```
+
+## Quality Standards
+- All commands have --help documentation
+- Unit tests for storage module
+- Integration tests for CLI commands

examples/simple-cli-tool/.ralph/fix_plan.md

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+# Fix Plan - Todo CLI
+
+## Priority 1: Foundation
+- [ ] Set up package.json with commander and jest dependencies
+- [ ] Create src/storage.js with load/save functions for ~/.todos.json
+- [ ] Create src/index.js entry point with commander setup
+
+## Priority 2: Core Commands
+- [ ] Implement `todo add "description"` command
+- [ ] Implement `todo list` command with status indicators
+- [ ] Implement `todo complete <id>` command
+- [ ] Implement `todo delete <id>` command
+
+## Priority 3: Polish
+- [ ] Add comprehensive --help text for each command
+- [ ] Handle edge cases (empty list, invalid ID, negative ID)
+- [ ] Write unit tests for storage.js module
+- [ ] Write integration tests for CLI commands
+- [ ] Add a `todo clear` command to remove all completed tasks
+
+## Discovered
+<!-- Ralph will add discovered tasks here -->

examples/simple-cli-tool/README.md

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+# Example: Simple CLI Tool
+
+This example shows a minimal Ralph configuration for a command-line todo application built with Node.js.
+
+## What This Example Demonstrates
+
+- **Minimal PROMPT.md** - Just enough context for a focused project
+- **Specific fix_plan.md** - Concrete, actionable tasks
+- **No specs/ needed** - Simple enough that PROMPT.md covers everything
+
+## Project Structure
+
+```
+simple-cli-tool/
+├── .ralph/
+│   ├── PROMPT.md        # Project goals and principles
+│   └── fix_plan.md      # Task list
+├── .ralphrc             # Configuration (auto-generated)
+└── README.md            # This file
+```
+
+## How to Use This Example
+
+1. Copy this directory to a new location:
+   ```bash
+   cp -r examples/simple-cli-tool ~/my-todo-app
+   cd ~/my-todo-app
+   ```
+
+2. Initialize git and npm:
+   ```bash
+   git init
+   npm init -y
+   ```
+
+3. Run Ralph:
+   ```bash
+   ralph --monitor
+   ```
+
+## Key Points
+
+### PROMPT.md is Focused
+
+Notice how PROMPT.md:
+- States exactly what the tool should do
+- Specifies the technology (Node.js, commander.js)
+- Defines key behaviors (where data is stored, error handling)
+
+### fix_plan.md Uses Priorities
+
+Tasks are grouped by priority:
+- Priority 1: Foundation (must work before anything else)
+- Priority 2: Core features (the main functionality)
+- Priority 3: Polish (nice-to-have improvements)
+
+### No specs/ Directory
+
+This project is simple enough that PROMPT.md provides all necessary context. specs/ would be overkill here.
+
+## When to Add More Files
+
+Consider adding specs/ if you need:
+- Complex command behavior documentation
+- Data format specifications
+- External service integration details
+
+For this simple example, PROMPT.md is sufficient.