Bump KUDO and update README

Signed-off-by: Jan Schlicht <[email protected]>

Author: Jan Schlicht

README.md

@@ -5,8 +5,38 @@
 
 `kitt` synchronizes KUDO repositories from an index of _operator package references_.
 
+A list of YAML files describing _operator package references_ is used to create or update a [KUDO operator repository](https://github.com/kudobuilder/kudo/blob/main/keps/0015-repository-management.md) on the local file system.
+
 Example usage:
 
+```shell
+kitt update --repository /var/kudo/repo /var/kudo/operators/*.yaml
 ```
-kitt update --repository /var/kudo/repo $(git diff --name-only --diff-filter=AM)
+
+## Operator package references
+
+`kitt` builds the KUDO repository from references to operator packages. Each reference describes how to retrieve one or more versioned packages of an operator.
+
+Consider an operator that is developed in a Git repository. The actual operator package (`operator.yaml`, `parameters.yaml`, ...) is in the `operator` folder of this repository. Tagged versions of this operator are then referenced by the following YAML:
+
+```yaml
+apiVersion: index.kudo.dev/v1alpha1
+kind: Operator
+name: MyOperator
+git-sources:
+- name: my-git-repository
+  url: https://github.com/example/myoperator.git
+versions:
+- version: "1.0.0"
+  git:
+    source: my-git-repository
+    directory: operator
+    tag: "v1.0.0"
+- version: "2.0.0"
+  git:
+    source: my-git-repository
+    directory: operator
+    tag: "v2.0.0"
 ```
+
+Running `kitt update` with this YAML as an argument will check out the referenced Git repository with the specified tags `v1.0.0` and `v2.0.0`, build tarballs from the operator package in the `operator` folder, and add these tarballs to a KUDO repository.

go.mod

@@ -4,7 +4,7 @@ go 1.14
 
 require (
 	github.com/Masterminds/semver v1.5.0
-	github.com/kudobuilder/kudo v0.14.0
+	github.com/kudobuilder/kudo v0.15.0
 	github.com/sirupsen/logrus v1.6.0
 	github.com/spf13/afero v1.3.1
 	github.com/spf13/cobra v1.0.0