update readme

Author: idealvin

readme.md

@@ -429,6 +429,13 @@ xmake -a   # build all projects (libco, gen, co/test, co/unitest)
 ```
 
 
+#### Build shared library
+
+```sh
+xmake f -k shared
+xmake -v
+```
+
 #### Build with mingw
 
 ```sh
@@ -496,6 +503,13 @@ make install
 ```
 
 
+#### Build shared library
+
+```sh
+cmake .. -DBUILD_SHARED_LIBS=ON
+```
+
+
 #### install libco from vcpkg
 
 ```sh