Update documentation link to point to new portal

Author: pglombardo

README.md

@@ -66,7 +66,7 @@ This Python package supports [OpenTracing](http://opentracing.io/).
 
 ## Documentation
 
-You can find more documentation covering supported components and minimum versions in the Instana [documentation portal](https://instana.atlassian.net/wiki/display/DOCS/Python).
+You can find more documentation covering supported components and minimum versions in the Instana [documentation portal](https://docs.instana.io/).
 
 ## Contributing