docs: add sample code for ngx.process's get_master_pid() function.

Signed-off-by: Yichun Zhang (agentzh) <[email protected]>

Author: chronolaw

README.markdown

@@ -161,6 +161,8 @@ API Implemented
 * [ngx.shared.DICT.free_space](https://github.com/openresty/lua-nginx-module#ngxshareddictfree_space)
 * [ngx.shared.DICT.capacity](https://github.com/openresty/lua-nginx-module#ngxshareddictcapacity)
 
+[Back to TOC](#table-of-contents)
+
 ## resty.core.var
 
 * [ngx.var.VARIABLE](https://github.com/openresty/lua-nginx-module#ngxvarvariable)

lib/ngx/process.md

@@ -32,8 +32,7 @@ The API is still in flux and may change in the future without notice.
 Synopsis
 ========
 
-Enables privileged agent process and get process type
------------------------------------------------------
+Enables privileged agent process, gets process type, and then gets the master process PID:
 
 ```nginx
 # http config
@@ -61,6 +60,7 @@ server {
         content_by_lua_block {
             local process = require "ngx.process"
             ngx.say("process type: ", process.type())
+            ngx.say("master process pid: ", process.get_master_pid() or "-")
         }
     }
 }
@@ -80,6 +80,7 @@ The example location above produces the following response body:
 
 ```
 process type: worker
+master process pid: 8261
 ```
 
 [Back to TOC](#table-of-contents)