docs: refine documentation structure and language consistency

- Updated the tagline in `docusaurus.config.js` for improved clarity.
- Streamlined sidebar navigation items for better organization of player and developer resources.
- Enhanced README and various documentation files to clarify repository layout and improve accessibility.
- Standardized language to English across documentation, ensuring consistency and clarity.
- Removed unnecessary German localization references to focus on English content.

This commit aims to enhance the overall clarity and usability of the documentation.

sidebars.js

@@ -58,11 +58,7 @@ const sidebars = {
         {
           type: 'category',
           label: 'Tools & operations',
-          items: [
-            'meta/Steam-Workshop-and-Tooling',
-            'meta/devserver-betas',
-            'meta/IDEA_BACKLOG',
-          ],
+          items: ['meta/Steam-Workshop-and-Tooling', 'meta/devserver-betas', 'meta/IDEA_BACKLOG'],
         },
         {
           type: 'category',