docs: update installation guide with npx support

- Add npx bmad-method agent-install option for users without cloned repo
- Show both local and npx commands side by side
- Clarify when to use each installation option
- Update automatic updates section with npx option
- Add prominent note about npx capability

Users can now install custom agents without needing to clone the BMAD repository.

src/modules/bmb/workflows/create-agent/installation-guide.md

@@ -0,0 +1,76 @@
+# Installing Your Custom Agent
+
+Your agent YAML file is a template that gets compiled to a runnable Markdown (.md) file with XML.
+
+**Good news**: You can install agents without cloning the BMAD repository using `npx bmad-method`!
+
+## Installation Options
+
+### Option 1: Interactive Install (Recommended)
+
+```bash
+# From your BMAD project directory
+# Option A: If you have BMAD installed locally
+bmad agent-install
+
+# Option B: If you don't have BMAD cloned (works anywhere!)
+npx bmad-method agent-install
+
+# Follow the prompts to select and install your agent
+```
+
+**Best for**: Installing individual agents with custom naming and target selection
+
+### Option 2: Batch Install
+
+1. **Copy** your agent YAML to `{project}/.bmad/custom/src/agents/`
+2. **Run** the installer and select "Compile Agents (Quick rebuild of all agent .md files)"
+
+**Best for**: Installing multiple agents at once or rebuilding all custom agents
+
+## What Happens During Installation
+
+1. **Source**: Your agent YAML (from `custom/src/agents/`)
+2. **Compile**: Gets converted to executable .md format
+3. **Install**: Copied to `custom/agents/{agent-name}/`
+4. **Register**: Added to agent manifest and IDE commands
+5. **Backup**: Source saved to `_cfg/custom/agents/` for updates
+
+## Automatic Updates
+
+**For individual agents**:
+
+```bash
+bmad agent-install              # If BMAD installed locally
+npx bmad-method agent-install    # Works anywhere without cloning
+```
+
+**For all agents (including custom ones)**:
+
+- `bmad install` → "Compile Agents" (rebuild all agents)
+- `bmad install` → "Quick Update" (during upgrades)
+
+**When to use which**:
+
+- **Option 1**: Best for new agents or when you want custom persona names
+- **Option 2**: Best for bulk updates or when you've modified YAML files directly
+
+## File Structure
+
+```
+custom/
+├── src/agents/          # Your source YAMLs (BMB builder output)
+└── agents/              # Installed compiled agents
+    └── my-agent/
+        └── my-agent.md  # Runnable agent
+
+_cfg/custom/agents/      # Backup copies for updates
+```
+
+## Target Projects
+
+You can install agents to:
+
+- Current project (default)
+- Any other BMAD project on your system
+- Custom directory (for sharing agents)