Add io.openlock documentation

manual/builtin_modules.md

@@ -1197,6 +1197,7 @@ The io operation module extends lua's built-in io module to provide more easy-to
 | [io.printf](#ioprintf) | No line formatted output to file | >= 2.0.1 |
 | [io.lines](#iolines) | Read all lines from file | >= 2.2.9 |
 | [io.stdfile](#iostdfile) | Get std file | >= 2.2.9 |
+| [io.openlock](#ioopenlock) | Open a lock of a file | >= 2.2.9 |
 
 #### io.open
 
@@ -1373,6 +1374,16 @@ io.stdfile("/dev/stdout")
 io.stdfile("/dev/stderr")
 ```
 
+### io.openlock
+
+- Open a lock of a file
+
+Returns a file lock object when successfully locking the file
+
+```lua
+io.openlock("xxx.txt")
+```
+
 ### path
 
 The path operation module implements cross-platform path operations, which is a custom module of xmake.