fix(docs): document pnpm instead of yarn

docs/content/doc/development/development.md

@@ -36,8 +36,9 @@ Make sure to check the other doc articles for specific development tasks like [t
 ## Frontend requirements
 
 The code for the frontend is located at [code.vikunja.io/frontend](https://code.vikunja.io/frontend).
+More instructions can be found in the repo's README.
 
-You need to have yarn v1 and nodejs in version 16 installed.
+You need to have [pnpm](https://pnpm.io/) and nodejs in version 16 or 18 installed.
 
 ## Git flow
 

docs/content/doc/development/test.md

@@ -98,12 +98,12 @@ Check out the docs [in the frontend repo](https://kolaente.dev/vikunja/frontend/
 To run the frontend unit tests, run
 
 {{< highlight bash >}}
-yarn test:unit
+pnpm test:unit
 {{< /highlight >}}
 
 The frontend also has a watcher available that re-runs all unit tests every time you change something.
 To use it, simply run
 
 {{< highlight bash >}}
-yarn test:unit-watch
+pnpm test:unit-watch
 {{< /highlight >}}