expand concepts section

docs/concepts/EvictionAndDisruptionBudget/README.md

@@ -2,8 +2,6 @@
 
 ## Overview
 
-In the context of fleet, 
-
 `Eviction` pertains to act to removing resources from a target cluster propagated by a resource placement object from the hub cluster.
 
 `Placement Disruption Budget` object protects against voluntary disruption and in case of fleet the only allowed voluntary disruption as of now is eviction.
@@ -16,7 +14,7 @@ As mentioned the creation of an eviction object indicates that resources need to
 
 To successfully evict resources from a cluster the user needs to specify,
 
-- The name of the `ClusterResourcePlacement` which propagated resources to target cluster
+- The name of the `Placement` object which propagated resources to target cluster
 - The name of the target cluster from which we need to evict resources.
 
 When specifying `ClusteResourcePlacement` object in eviction's spec the user needs to consider the following cases,
@@ -27,5 +25,23 @@ When specifying `ClusteResourcePlacement` object in eviction's spec the user nee
 > **Note:** After an eviction is executed there is no guarantee that the cluster won't be picked again by the scheduler to propagate resources for a `ClusterResorucePlacement`. 
 > The user needs to specify a taint on the cluster in order to prevent the scheduler from picking the cluster again.
 
-## Disruption Budget
+## ClusterResourcePlacementDisruptionBudget
+
+The `ClusterResourcePlacementDisruptionBudget` is used protect resources propagated by a `ClusterResourcePlacement` to a target cluster from voluntary disruption i.e. `eviction`.
+
+> **Note:** When specifying a `ClusterResourcePlacementDisruptionBudget` the name should be the same as the `ClusterResourcePlacement` that it's trying to protect.
+
+Users are allowed to specify one of two fields in `ClusterResourcePlacementDisruptionBudget` spec since they are mutually exclusive,
+
+- MaxUnavailable - specifies the maximum number of clusters in which a placement can be unavailable due to voluntary disruptions.
+- MinAvailable - specifies the minimum number of cluster in which placements are available despite voluntary disruptions.
+
+> **Note:** For both MaxUnavailable and MinAvailable involuntary disruption are not subject to the disruption budget but will still count against it.
+
+When specifying a disruption budget for a particular `ClusterResourcePlacement` the user needs to consider the following cases,
+
+- For `PickFixed` CRP, if a `ClusterResourcePlacementDisruptionBudget` is specified or not, if an eviction is carried out the user will receive an invalid eviction error message in the eviction status
+- For `PickAll` CRP, if a `ClusterResourcePlacementDisruptionBudget` is specified and `MaxUnavailable` field is set the user will receive a misconfigured placement disruption budget error message in the eviction status
+- For `PickN` CRP, if a `ClusterResourcePlacementDisruptionBudget` is specified the user can either set `MaxUnavailable` or `MinAvailable`
+