docs: one manager cannot run both sharded and non-sharded controllers (#443)

Author: timebertt

README.md

@@ -22,6 +22,9 @@ I completed a study project ("half-time thesis") on this topic and evolved it in
 
 This repository contains the implementation belonging to the scientific work: the actual sharding implementation, a sample operator using controller sharding, a monitoring and continuous profiling setup, and some tools for development and evaluation purposes.
 
+Since finishing the scientific work, this project evolved further, especially in the [v0.9 release](https://github.com/timebertt/kubernetes-controller-sharding/releases/tag/v0.9.0).
+Be aware that the Master's thesis might not reflect the current development state in all descriptions.
+
 ## Motivation 💡
 
 Typically, [Kubernetes controllers](https://kubernetes.io/docs/concepts/architecture/controller/) use a leader election mechanism to determine a *single* active controller instance (leader).

docs/implement-sharding.md

@@ -163,6 +163,8 @@ func run() error {
 }
 ```
 
+Note that if you're using controller-runtime, the same manager instance cannot run sharded and non-sharded controllers as a manager can only run under a single resource lock (either leader election or shard lease).
+
 ### Filtered Watch Cache
 
 In short: use the following label selector on watches for all sharded resources listed in the `ControllerRing`.