docs(welcome): restructure documentation directories and add new guides section

docs/guides/index.mdx

@@ -0,0 +1,11 @@
+---
+title: Guides
+description: News and writing from the team.
+type: blog
+---
+
+<CardGroup cols={2}>
+  <Card title="Introducing Blume" href="/blog/introducing-blume">
+    Why we built a markdown-first docs framework.
+  </Card>
+</CardGroup>

docs/guides/introducing-blume.mdx

@@ -0,0 +1,8 @@
+---
+title: Introducing Blume
+type: blog
+date: 2026-06-22
+description: Why we built a markdown-first docs framework.
+---
+
+Documentation should be fast, AI-ready, and zero-config — down to not needing a starter template at all. Here's the thinking behind Blume.