doc: add prefix `prefix` when require Lua library . (#47)

diff --git a/README.md b/README.md
index a0a8977..9e69551 100644
--- a/README.md
+++ b/README.md
@@ -32,7 +32,7 @@
         -- Instance means the number of Nginx deployment, does not mean the worker instances
         metadata_buffer:set('serviceInstanceName', 'User Service Instance Name')
 
-        require("client"):startBackendTimer("http://127.0.0.1:8080")
+        require("skywalking.client"):startBackendTimer("http://127.0.0.1:8080")
     }
 
     server {
@@ -120,10 +120,10 @@
 The following APIs are for developers or using this lib out of the Nginx case.
 
 ## Nginx APIs
-- **startTimer**, `require("client"):startBackendTimer("http://127.0.0.1:8080")`. Start the backend timer. This timer register the metadata and report traces to the backend.
-- **start**, `require("tracer"):start("upstream service", correlation)`. Begin the tracing before the upstream begin. The custom data (table type) can be injected as the second parameter, and then they will be propagated to the downstream service.
-- **finish**, `require("tracer"):finish()`. Finish the tracing for this HTTP request.
-- **prepareForReport**, `require("tracer"):prepareForReport()`. Prepare the finished segment for further report.
+- **startTimer**, `require("skywalking.client"):startBackendTimer("http://127.0.0.1:8080")`. Start the backend timer. This timer register the metadata and report traces to the backend.
+- **start**, `require("skywalking.tracer"):start("upstream service", correlation)`. Begin the tracing before the upstream begin. The custom data (table type) can be injected as the second parameter, and then they will be propagated to the downstream service.
+- **finish**, `require("skywalking.tracer"):finish()`. Finish the tracing for this HTTP request.
+- **prepareForReport**, `require("skywalking.tracer"):prepareForReport()`. Prepare the finished segment for further report.
 
 ## Tracing APIs at LUA level
 **TracingContext** is the entrance API for lua level tracing.
diff --git a/examples/nginx.conf b/examples/nginx.conf
index 7c61b00..b9a74bf 100644
--- a/examples/nginx.conf
+++ b/examples/nginx.conf
@@ -38,7 +38,7 @@
         -- Instance means the number of Nginx deloyment, does not mean the worker instances
         metadata_buffer:set('serviceInstanceName', 'User Service Instance Name')
 
-        require("client"):startBackendTimer("http://127.0.0.1:8080")
+        require("skywalking.client"):startBackendTimer("http://127.0.0.1:8080")
     }
 
     server {