docs: reorganize upgrade documentation structure

- Rename docs/upgrading-spec-kit.md to docs/upgrade.md for brevity
- Update README and documentation index links to point to new upgrade guide
- Update table of contents to use shorter "Upgrade" title
- Simplify section headers in upgrade guide
- Add Getting Started section back to docs/index.md with upgrade guide link

Commit-generated-by: GitHub Copilot <github.copilot@github.com>
Signed-off-by: Ashley Childress <6563688+anchildress1@users.noreply.github.com>

docs/index.md

@@ -8,6 +8,13 @@
 
 Spec-Driven Development **flips the script** on traditional software development. For decades, code has been king — specifications were just scaffolding we built and discarded once the "real work" of coding began. Spec-Driven Development changes this: **specifications become executable**, directly generating working implementations rather than just guiding them.
 
+## Getting Started
+
+- [Installation Guide](installation.md)
+- [Quick Start Guide](quickstart.md)
+- [Upgrade Guide](upgrade.md)
+- [Local Development](local-development.md)
+
 ## Core Philosophy
 
 Spec-Driven Development is a structured process that emphasizes:

docs/toc.yml

@@ -9,8 +9,8 @@
       href: installation.md
     - name: Quick Start
       href: quickstart.md
-    - name: Upgrading Spec Kit
-      href: upgrading-spec-kit.md
+    - name: Upgrade
+      href: upgrade.md
 
 # Development workflows
 - name: Development

docs/upgrade.md

@@ -1,4 +1,4 @@
-# Upgrading Spec Kit
+# Upgrade Guide
 
 > You have Spec Kit installed and want to upgrade to the latest version to get new features, bug fixes, or updated slash commands. This guide covers both upgrading the CLI tool and updating your project files.
 
@@ -14,7 +14,7 @@
 
 ---
 
-## Part 1: Upgrading the CLI Tool
+## Part 1: Upgrade the CLI Tool
 
 The CLI tool (`specify`) is separate from your project files. Upgrade it to get the latest features and bug fixes.