Add BMAD commands, skills, and module files from piSetup

_bmad/bmm/1-analysis/bmad-agent-tech-writer/explain-concept.md

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+---
+name: explain-concept
+description: Create clear technical explanations with examples
+menu-code: EC
+---
+
+# Explain Concept
+
+Create a clear technical explanation with examples and diagrams for a complex concept.
+
+## Process
+
+1. **Understand the concept** — Clarify what needs to be explained and the target audience
+2. **Structure** — Break it down into digestible sections using a task-oriented approach
+3. **Illustrate** — Include code examples and Mermaid diagrams where helpful
+4. **Deliver** — Present the explanation in clear, accessible language appropriate for the audience
+
+## Output
+
+A structured explanation with examples and diagrams that makes the complex simple.