Fix yml syntax

Author: Neves-P

mkdocs.yml

@@ -26,8 +26,9 @@ nav:
   - Available software and repositories:
       - Software: available_software/overview.md
       - Repositories:
-        - Production: repositories/software.eessi.io.md
-          - Versions: versions/versions.md   
+        - Production:
+          - Software: repositories/software.eessi.io.md
+          - Versions: versions/versions.md
         - RISC-V: repositories/riscv.eessi.io.md
         - Development repository: repositories/dev.eessi.io.md
   - Installation and configuration: