Readme: Fix broken API documentation link on Readme (#4942)

Author: apurv-1

README.md

@@ -58,7 +58,7 @@ via Github pull requests.
 * Developer [wiki](https://cwiki.apache.org/confluence/display/CLOUDSTACK/Home)
 * [Release notes](http://docs.cloudstack.apache.org/projects/cloudstack-release-notes)
 * Design [documents](https://cwiki.apache.org/confluence/display/CLOUDSTACK/Design)
-* API [documentation](http://cloudstack.apache.org/docs/api)
+* API [documentation](https://cloudstack.apache.org/api.html)
 * How to [contribute](CONTRIBUTING.md)
 
 ## Getting Involved and Contributing