added build instructions

build.json

@@ -0,0 +1,19 @@
+{
+	"variables" : {
+		"id" : "84127ecc-6892-4c63-8860-16a4f491fe4c"
+	},
+	"builders": [
+		{
+        	"type": "lxd",
+        	"name": "focal-fossa",
+        	"image": "ubuntu:20.04",
+        	"output_image": "focal-fossa:{{user `id`}}",
+        	"publish_properties": {
+          		"description": "This is a default empty Ubuntu 20.04 (\"Focal Fossa\") Runtime provided as LXD container."
+"
+        	}
+      	}
+    ],
+    "provisioners": [],
+    "post-processors": []
+}