update README.md: add github actions build status

cw1997 · web-flow · commit a8ce719c90d0 · 2021-10-04T03:36:21.000+08:00
diff --git a/README.md b/README.md
@@ -1,4 +1,6 @@
 # inetutils
+[![CMake](https://github.com/cw1997/inetutils/actions/workflows/cmake.yml/badge.svg)](https://github.com/cw1997/inetutils/actions/workflows/cmake.yml)
+
 Some network utils including 'ping' and 'traceroute'
 
 # build
