badges-backend: refactoring and support returning json as well as svg image.

Signed-off-by: Andreas Stenius <git@astekk.se>

plugins/badges-backend/README.md

@@ -1,10 +1,30 @@
 # Badges Backend
 
-Simple plugin for serving badges.
+Backend plugin for serving badges. Default implementation uses
+[badge-maker](https://www.npmjs.com/package/badge-maker) for creating
+the badges, in svg.
 
 ## Setup
 
-N/A
+Define which badges to offer in the backend api by declaring them in
+the app-config, under a `badges` key. Example:
+
+```yaml
+badges:
+  docs:
+    kind: 'entity'
+    target: '_{entity_url}/docs'
+    label: 'Documentation'
+    message: '_{entity.metadata.name}'
+    color: 'navyblue'
+
+  lifecycle:
+    kind: 'entity'
+    description: 'Entity lifecycle badge'
+    target: '_{entity_url}'
+    label: 'Lifecycle'
+    message: '_{entity.spec.lifecycle}'
+```
 
 ## Links