docs: restore FAQ index page

Re-add the FAQ index page that was accidentally deleted, with
updated repo-relative link format.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/explanation/faq/index.md

@@ -0,0 +1,16 @@
+---
+title: "Frequently Asked Questions"
+description: Frequently asked questions about the BMad Method
+---
+
+Quick answers to common questions about the BMad Method, organized by topic.
+
+## Topics
+
+- [Getting Started](/docs/explanation/faq/getting-started-faq.md) - Questions about starting with BMad
+- [Levels & Tracks](/docs/explanation/faq/levels-and-tracks-faq.md) - Choosing the right level
+- [Workflows](/docs/explanation/faq/workflows-faq.md) - Workflow and phase questions
+- [Planning](/docs/explanation/faq/planning-faq.md) - Planning document questions
+- [Implementation](/docs/explanation/faq/implementation-faq.md) - Implementation questions
+- [Brownfield](/docs/explanation/faq/brownfield-faq.md) - Existing codebase questions
+- [Tools & Advanced](/docs/explanation/faq/tools-faq.md) - Tools, IDEs, and advanced topics