Added description for webhook and workload (#32)

Signed-off-by: Florian Bacher <florian.bacher@dynatrace.com>

README.md

@@ -37,6 +37,27 @@ The mutating webhook works only on resources that have Keptn annotations.
 The mutation consists in changing the scheduler used for the deployment with the Keptn Scheduler.
 The webhook should be as fast as possible and should not create/change any resource.
 
+When the webhook receives a request for a new pod, it will look for the following annotations:
+
+```
+keptn.sh/application (optional)
+keptn.sh/workload
+```
+
+Additionally, it will compute a version string, using a hash function that takes certain properties of the pod as parameters
+(e.g. the images of its containers).
+Next, it will look for an existing instance of a `Workload CRD` for the given workload name:
+
+- If it finds the `Workload`, it will update its version according to the previously computed version string. In addition, it will include a reference to the ReplicaSet UID of the pod (i.e. the Pods owner), or the pod itself, if it does not have an owner.
+- If it does not find a workload instance, it will create one containing the previously computed version string. In addition, it will include a reference to the ReplicaSet UID of the pod (i.e. the Pods owner), or the pod itself, if it does not have an owner. 
+It will use the following annotations for
+the specification of the pre/post deployment checks that should be executed for the `Workload`:
+  - `keptn.sh/pre-deployment-tasks: task1,task2`
+  - `keptn.sh/post-deployment-tasks: task1,task2`
+
+
+After either one of those actions has been taken, the webhook will set the scheduler of the pod and allow the pod to be scheduled.
+
 
 ### Scheduler
 
@@ -48,7 +69,16 @@ tbd
 
 ### Workload
 
-tbd
+A Workload contains information about which tasks should be performed during the `preDeployment` as well as the `postDeployment`
+phase of a deployment. In its state it keeps track of the currently active `Workload Instances`, which are responsible for doing those checks for
+a particular instance of a Deployment/StatefulSet/ReplicaSet (e.g. a Deployment of a certain version). 
+
+### Workload Instance
+
+A Workload Instance is responsilbe for executing the pre- and post deployment checks of a workload. In its state, it keeps track of the current status of all checks, as well as the overall state of
+the Pre Deployment phase, which can be used by the scheduler to tell that a pod can be allowed to be placed on a node.
+Workload Instances have a reference to the respective Deployment/StatefulSet/ReplicaSet, to check if it has reached the desired state. If it detects that the referenced object has reached
+its desired state (e.g. all pods of a deployment are up and running), it will be able to tell that a `PostDeploymentCheck` can be triggered.
 
 ### Task