How to make your forum site show up on google search
Please read this article, it should be helpful:
In case you want to say thank you !)
We'd really appreciate and be thankful if you leave a good review on plugin page. This is the best way to say thank you to this project and support team.
If you use Google webmaster tools to submit your sitemap, then nothing else is needed (in robots.txt).
Also submiting a sitemap doesn't mean your site is/will be indexed or when it will be indexed.
If your site is new, then you will not see any indexing unless some content is posted. And that indexing can take months, and ranking for something can take a long time.