Add .asf.yaml based on Apache's new website publishing procedures

Starting on July 1st, this file will be needed in order for any
new commits to asf-site to show up at https://madlib.apache.org

The second block adds a new feature, which allows us to test
changes in any branch without overwriting the official webpage,
by pushing it to asf-staging and viewing it at:
 https://madlib.staged.apache.org

Based on instructions here:
https://cwiki.apache.org/confluence/display/INFRA/Git+-+.asf.yaml+features#Git.asf.yamlfeatures-WebSiteDeploymentServiceforGitRepositories
1 file changed