Move getting-started.md to quickstart folder and update references in mkdocs.yml

doc.zih.tu-dresden.de/docs/training/getting_started.md → doc.zih.tu-dresden.de/docs/quickstart/getting_started.md

-# Getting Started
+# Quick Start
 
 This page is intended to provide the key information on starting to work on the ZIH High
 Performance Computing (HPC) system and is of particular importance to new users.

doc.zih.tu-dresden.de/mkdocs.yml

 nav:
   - Home: index.md
+  - Quick start: quickstart/getting_started.md
   - Application for Login and Resources:
     - Overview: application/overview.md
     - Terms of Use: application/terms_of_use.md
@@ -102,8 +103,6 @@ nav:
       - Binding And Distribution Of Tasks: jobs_and_resources/binding_and_distribution_of_tasks.md
   - Support:
     - How to Ask for Support: support/support.md
-  - Training:
-    - Getting Started: training/getting_started.md
   - Archive of the Old Wiki:
     - Overview: archive/overview.md
     - Bio Informatics: archive/bioinformatics.md