add screenshots to plugin.json

Author: hoptical

src/plugin.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://raw.githubusercontent.com/grafana/grafana/master/docs/sources/developers/plugins/plugin.schema.json",
   "type": "datasource",
-  "name": "Node Graph API Plugin",
+  "name": "Node Graph API Datasource Plugin",
   "id": "hamedkarbasi93-nodegraphapi-datasource",
   "metrics": true,
   "info": {
@@ -10,7 +10,11 @@
       "name": "Hamed Karbasi",
       "url": "https://grafana.com/orgs/hamedkarbasi93"
     },
-    "keywords": ["nodegraph", "datasource", "api"],
+    "keywords": [
+      "nodegraph",
+      "datasource",
+      "api"
+    ],
     "logos": {
       "small": "img/logo.svg",
       "large": "img/logo.svg"
@@ -25,7 +29,16 @@
         "url": "https://github.com/exaco/nodegraph-api-plugin/blob/master/LICENSE"
       }
     ],
-    "screenshots": [],
+    "screenshots": [
+      {
+        "name": "Add Datasource",
+        "path": "img/add-datasource.png"
+      },
+      {
+        "name": "Graph Example",
+        "path": "img/graph-example.png"
+      }
+    ],
     "version": "0.1.0",
     "updated": "%TODAY%"
   },