Publish to Netbeans Plugin Portal

This is issue is to document any additional process and deploy a given release nbm to the [Netbeans Plugin Portal](https://plugins.netbeans.apache.org/?search=python&nbv=&cat=).

For more details see https://cwiki.apache.org/confluence/display/NETBEANS/How+to+get+plugin+on+Plugin+Portal+Update+Center