Update the TOC (#238)

Update mkdocs-base.yml

Author: alina-derkach-oaza

mkdocs-base.yml

@@ -193,16 +193,16 @@ nav:
       - 2018 (8.0.4 - 8.0.3-rc1):
         - release-notes/8.0/8.0.4.md
         - release-notes/8.0/8.0-3-rc1.md
-  - Discover Percona XtraBackup:
-      - about-xtrabackup.md
-      - how-xtrabackup-works.md
-      - xtrabackup-version-numbers.md
-  -  Quickstart Guide:
+  - Quickstart Guide:
       - quickstart-overview.md
       - quickstart-docker.md
       - quickstart-restore-backup.md
       - quickstart-exit.md
       - quickstart-next-steps.md
+  - How Percona XtraBackup works:
+      - about-xtrabackup.md
+      - how-xtrabackup-works.md
+      - xtrabackup-version-numbers.md
   - Features:
       - Backup features:
         - lru-dump-backup.md