[cwrap] Update README.md (#3324)

This commit will update README.md

Signed-off-by: Seok NamKoong <sk.namkoong@samsung.com>

diff --git a/contrib/cwrap/README.md b/contrib/cwrap/README.md
index f4f44b0..64c8084 100644 (file)
--- a/contrib/cwrap/README.md
+++ b/contrib/cwrap/README.md
@@ -1,3 +1,25 @@
-## What is "cwrap"?
+## cwrap
+
+### Purpose
 
 _cwrap_ is a collection of C++ wrappers for POSIX C API.
+
+### How to use
+
+Currently it supports only file descriptor.
+
+### Example
+- File Descriptor
+
+```cpp
+cwrap::Fildes fildes{open(path.c_str(), O_RDONLY)};
+
+if (fildes.get() < 0)
+{
+    std::ostringstream ostr;
+    ostr << "Error: " << path << " not found" << std::endl;
+    throw std::runtime_error{ostr.str()};
+}
+
+google::protobuf::io::FileInputStream fis(fildes.get());
+```