Add demo for xvfb.

demos/xvfb/README.md

@@ -0,0 +1,24 @@
+# Configure xvfb tool installation
+
+Basic configuration of the [xvfb](https://plugins.jenkins.io/xvfb/)
+
+## sample configuration
+
+For plugin version 1.1:
+
+```yaml
+tool:
+  xvfbInstallation:
+    installations:
+      - name: "default"
+```
+
+For plugin version 1.2 and up:
+
+```yaml
+tool:
+  xvfb:
+    installations:
+      - name: "default"
+        home: ""
+```