Update README.md

Author: sea5kg

README.md

@@ -1,5 +1,11 @@
 # wsjcpp-core
 
+<p align="center">
+    <a href="https://github.com/wsjcpp/wsjcpp-core/pulse" alt="Activity">
+        <img src="https://img.shields.io/github/commit-activity/m/wsjcpp/wsjcpp-core" />
+    </a>
+</p>
+
 [![Build Status](https://api.travis-ci.org/wsjcpp/wsjcpp-core.svg?branch=master)](https://travis-ci.org/wsjcpp/wsjcpp-core) [![Github Stars](https://img.shields.io/github/stars/wsjcpp/wsjcpp-core.svg?label=github%20%E2%98%85)](https://github.com/wsjcpp/wsjcpp-core/stargazers) [![Github Stars](https://img.shields.io/github/contributors/wsjcpp/wsjcpp-core.svg)](https://github.com/wsjcpp/wsjcpp-core/) [![Github Forks](https://img.shields.io/github/forks/wsjcpp/wsjcpp-core.svg?label=github%20forks)](https://github.com/wsjcpp/wsjcpp-core/network/members)
 [![Language grade: C/C++](https://img.shields.io/lgtm/grade/cpp/g/wsjcpp/wsjcpp-core.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/wsjcpp/wsjcpp-core/context:cpp) [![Total alerts](https://img.shields.io/lgtm/alerts/g/wsjcpp/wsjcpp-core.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/wsjcpp/wsjcpp-core/alerts/)
 
@@ -427,4 +433,4 @@ Recoursive remove dir (+ subdirs) and files
 if (WsjcppCore::recoursiveRemoveDir("./folder2")) {
     // everything removed
 }
-```
+```