Reorganized installation docs

mkdocs.yml

@@ -1,7 +1,13 @@
 site_name: NetBox
+
 pages:
     - 'Introduction': 'index.md'
-    - 'Getting Started': 'getting-started.md'
+    - 'Installation':
+        - 'PostgreSQL': 'installation/postgresql.md'
+        - 'NetBox': 'installation/netbox.md'
+        - 'Web Server': 'installation/web-server.md'
+        - 'Upgrading': 'installation/upgrading.md'
+        - 'Alternate Install: Docker': 'installation/docker.md'
     - 'Configuration': 'configuration.md'
     - 'Data Model':
         - 'Circuits': 'data-model/circuits.md'
@@ -10,3 +16,6 @@ pages:
         - 'Secrets': 'data-model/secrets.md'
         - 'Extras': 'data-model/extras.md'
     - 'API Integration': 'api-integration.md'
+
+markdown_extensions:
+    - admonition: