Add preliminary docs for resource sets

docs/resourcesets.md

+Resource sets (`appResourceSets` or `loadGenResourceSets`) describe a set of Kubernetes resources.
+
+They can be created from Kubernetes YAMl files placed in ConfigMaps or from files of the filesystem accessible by Theodolite.
+
+### Creating Resources from ConfigMaps
+
+```yaml
+- configMap:
+    name: "example-configmap"
+    files:
+        - "uc1-kstreams-deployment.yaml"
+```
+
+### Creating Resources from the Filesystem
+
+```yaml
+- fileSystem:
+    path: ./../../../../../../config
+    files:
+      - "uc1-kstreams-deployment.yaml"
+      - "aggregation-service.yaml"
+      - "jmx-configmap.yaml"
+      - "uc1-service-monitor.yaml"
+```