Reintroduce search bar 

The search bar was removed in to get a successful Vercel deployment in [this PR](https://github.com/zeitgeistpm/documentation/pull/89). The search bar should be reintroduced.

https://github.com/zeitgeistpm/documentation/pull/89/files#diff-a038096cbdea434999e1dce5ab497212f1fe18204dde1a027ce3bdd663261a2aL50-L63