removed yarn from docs

Signed-off-by: René <snooz@posteo.de>

Author: Snooz82

.github/.workflows/pages.yml

@@ -5,21 +5,27 @@ This website is built using [Docusaurus](https://docusaurus.io/), a modern stati
 ### Installation
 
 ```
-$ yarn
+$ npm install
+```
+
+For reproducible installs in CI, use:
+
+```
+$ npm ci
 ```
 
 ### Local Development
 
 ```
-$ yarn start
+$ npm run start
 ```
 
 This command starts a local development server and opens up a browser window. Most changes are reflected live without having to restart the server.
 
 ### Build
 
 ```
-$ yarn build
+$ npm run build
 ```
 
 This command generates static content into the `build` directory and can be served using any static contents hosting service.
@@ -29,13 +35,13 @@ This command generates static content into the `build` directory and can be serv
 Using SSH:
 
 ```
-$ USE_SSH=true yarn deploy
+$ USE_SSH=true npm run deploy
 ```
 
 Not using SSH:
 
 ```
-$ GIT_USER=<Your GitHub username> yarn deploy
+$ GIT_USER=<Your GitHub username> npm run deploy
 ```
 
 If you are using GitHub pages for hosting, this command is a convenient way to build the website and push to the `gh-pages` branch.