Document taint-based eviction (zalando#468)

* Document taint-based eviction

Author: sdudoladov

Diff for: docs/administrator.md

@@ -146,6 +146,11 @@ data:
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+Note that the Kubernetes version 1.13 brings [taint-based eviction](https://kubernetes.io/docs/concepts/configuration/taint-and-toleration/#taint-based-evictions) to the beta stage and enables it by default.
+Postgres pods by default receive tolerations for `unreachable` and `noExecute` taints with the timeout of `5m`.
+Depending on your setup, you may want to adjust these parameters to prevent master pods from being evicted by the Kubernetes runtime.
+To prevent eviction completely, specify the toleration by leaving out the `tolerationSeconds` value (similar to how Kubernetes' own DaemonSets are configured)
+
 ### Add cluster-specific labels
 
 In some cases, you might want to add `labels` that are specific to a given
@@ -197,6 +202,7 @@ spec:
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 ```
 
+
 ## Custom Pod Environment Variables
 
 It is possible to configure a ConfigMap which is used by the Postgres pods as