feat: Add cms-docs-common submodule to demonstrate config_file

Enhanced the example site to demonstrate the config_file feature:

- Added cms-docs-common as git submodule
- Updated mkdocs.yml to load CMS POG dropdown from shared config
- Now shows 3 dropdowns: 1 from config_file + 2 from mkdocs.yml
- Updated documentation to explain the mixed configuration approach

The example now demonstrates:
1. Loading shared config via git submodule (CMS POG Docs)
2. Adding site-specific dropdowns (Examples, Resources)
3. How both sources work together seamlessly

This provides a complete reference implementation for users.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: andrzejnovak

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "example/cms-docs-common"]
+	path = example/cms-docs-common
+	url = https://github.com/cms-cat/cms-docs-common.git

example/cms-docs-common

@@ -71,3 +71,22 @@ plugins:
   - header-dropdown:
       config_file: "shared-config/dropdowns.yml"
 ```
+
+**Live Example**: The "CMS POG Docs" dropdown in this site's header is loaded from the [cms-docs-common](https://github.com/cms-cat/cms-docs-common) repository via git submodule!
+
+## Mixing Configuration Sources
+
+You can combine shared config with site-specific dropdowns:
+
+```yaml
+plugins:
+  - header-dropdown:
+      config_file: "cms-docs-common/header-dropdown.yml"  # Shared
+      dropdowns:  # Site-specific
+        - title: "Local Links"
+          links:
+            - text: "About"
+              url: "/about/"
+```
+
+Both will appear in the header - check this example site to see it in action!

example/docs/getting-started.md

@@ -16,7 +16,13 @@ This plugin adds configurable dropdown menus to your MkDocs Material theme heade
 
 ## Check the Header!
 
-Look at the header above - you'll see example dropdown menus demonstrating the plugin's capabilities.
+Look at the header above - you'll see **three dropdown menus** demonstrating the plugin's capabilities:
+
+1. **CMS POG Docs** - Loaded from a shared configuration file via git submodule (`cms-docs-common`)
+2. **Examples** - Defined directly in `mkdocs.yml`
+3. **Resources** - Also defined directly in `mkdocs.yml`
+
+This demonstrates both configuration methods working together!
 
 ## Installation
 

example/docs/index.md

@@ -31,6 +31,7 @@ theme:
 plugins:
   - search
   - header-dropdown:
+      config_file: "cms-docs-common/header-dropdown.yml"
       dropdowns:
         - title: "Examples"
           links:
@@ -49,14 +50,6 @@ plugins:
             - text: "Material Theme Docs"
               url: "https://squidfunk.github.io/mkdocs-material/"
               target: "_blank"
-        - title: "Related Projects"
-          links:
-            - text: "MkDocs"
-              url: "https://www.mkdocs.org/"
-              target: "_blank"
-            - text: "Material for MkDocs"
-              url: "https://squidfunk.github.io/mkdocs-material/"
-              target: "_blank"
 
 markdown_extensions:
   - admonition