Fix WordPress links (GoogleCloudPlatform#662)

Author: bshaffer

appengine/wordpress/README.md

@@ -0,0 +1,11 @@
+# WordPress for Google App Engine
+
+Samples for deploying WordPress to App Engine.
+
+## Index
+
+|Runtime|Description|
+|---|---|
+|[php72](../php72/wordpress)| Sample and CLI tool for deploying WordPress to App Engine for PHP 7.2 (**recommended**)|
+|[flexible](../flexible/wordpress)|Sample and CLI tool for deploying WordPress to App Engine Flexible|
+|[php55](../php55/wordpress)| Sample and CLI tool for deploying WordPress to App Engine for PHP 5.5 (*deprecated*)|