Add installation docs

docs/installation.md

+---
+title: Installation
+has_children: false
+nav_order: 2
+---
+
+# Installing Theodolite
+
+The easiest option to install Theodolite is using [Helm](https://helm.sh).
+To install Theodolite with all its dependencies run:
+
+```sh
+helm repo add theodolite https://cau-se.github.io/theodolite
+helm repo update
+helm install theodolite theodolite/theodolite
+```
+
+This installs Theodolite in operator mode. Operator mode is the easiest to be used, but requires some permissions in the installation. If those cannot be granted, Theodolite can also be installed for standalone mode. 
+
+
+## Installation Options
+
+As usual, the installation via Helm can be configured by passing a values YAML file:
+
+```
+helm install theodolite theodolite/theodolite --values <your-config.yaml>
+```
+
+For this purpose the [default values file]() can serve as a template for your custom configuration.
+
+### Operator mode
+
+The Theodolite operator allows to run and manage benchmarks through the Kubernetes API. It is installed by setting `operator.enabled` to `true`. In addition to Theodolite's dependencies, this will deploy all resources that are required for the operator as well as the CRDs, users will interact with.
+
+**TODO:** link
+
+### Standalone mode
+
+For running Theodolite in standalone mode, it is sufficient to disable the operator by setting `operator.enabled` to `false`. With this setting, only Theodolite's dependencies as well as resources to get the necessary permissions are installed.
+
+### Random Scheduler
+
+Installation of the random scheduler can be enabled and via `randomScheduler.enabled`. Please note that the random scheduler is neither required in operator mode nor in standalone mode. However, it has to be installed if benchmark executions should use random scheduling.
+
+**TODO:** link
+
+### Multiple installations in the same cluster
+
+Multiple Theodolite installations in the same namespace are currently not fully tested.
+In cases, where you need to install multiple Theodolite instances, it's best to use dedicated namespaces **and** different release names.
+
+*Note that for meaningful results, usually only one benchmark should be executed at a time.*