Re-format example directory tree in README.md

Files in the exemplary tree were mis-aligned. So we replace it by the
output of `tree --dirsfirst`.

Change-Id: Ica4bdf811407e4af792e8bd1becf3083d126d24f
diff --git a/README.md b/README.md
index 2d2d339..7514661 100644
--- a/README.md
+++ b/README.md
@@ -47,11 +47,12 @@
 
 ```
 [workspace]/
-    WORKSPACE
-	BUILD
-    src/main/java/
-	src/main/resources/
-	[...]
+├── src
+│   └── main
+│       ├── java
+│       └── resources
+├── BUILD
+└── WORKSPACE
 ```
 
 To build this plugin, your `BUILD` can look like this: