add readme

Author: blackstorm

README.md

@@ -0,0 +1,10 @@
+## XA
+The `xa` example use http protocol for all rpc call.
+
+`tm` is a simaple transaction manager. There has 3 services: `api` and `customer` and `merchant`.
+
+### How to start
+```
+GET http://api:8080/order
+```
+`/order` api will call `customer` and `merchant` service.