How do you integrate a single JIRA project with JIRA Portfolio

[Martin Suntinger]

Just build a filter searching for all the issues of that JIRA project (Issues > Search for Issues > filter to the project > Save As..) use this filter to import the issues into Portfolio. 

Also, if you have existing versions (releases) you want to integrate, the recommendation is to import these first in the releases section before importing the issues, so that existing version assignments are kept upon issue import.