update readme

README.md

@@ -1,2 +1,19 @@
 # pybind11_demo
 
+# A demo shows how to write python with c++
+
+```python
+# make.py
+from pymake import *
+
+
+(
+    cmake("3.15")
+    .set("PYBIND11_FINDPYTHON", on)
+    .set(cmake_export_compile_commands, on)
+    .project("test_pybind11")
+    .find_package("pybind11","REQUIRED")
+    .pybind11_add_module(var(project_name),"main.cpp")
+    .write()
+)
+```