update release 2.6.0 with CDAP docker build info for developers

This is a different command than the one at 
http://stg-web101.sw.joyent.continuuity.net/cdap/2.7.0-SNAPSHOT/en/developers-manual/getting-started/standalone/docker.html
it is:
```
docker run -t -i -p 9999:9999 -p 10000:10000 caskdata/cdap-standalone
```

What should it be?