It is somewhat common to use develop or something similar as the main branch name. For pull request analysis it doesn't matter, since the hook events (of GitHub, GitLab, Bitbucket, Azure DevOps and Gerrit) give complete information for Softagram about the changes (base/head SHA1). So just for the sake of automated code review, this article is not relevant.
However, if you want to keep track of the architectural changes in your main branch, and have main branch model available for Softagram Desktop usage, it is good to explicitly define main branch name for Softagram. This happens by running below command on the server (no easier way yet available):
docker exec -ti softagram python3 ui/cli/softagramservice.py setup_analysis_target --project-id PROJECT --main-branch-name develop --branch-priority-list develop,master
Remember to replace PROJECT with the UUID of your project and to replace develop with your main branch name. You may have also several, and Softagram will try them on that order one by one to find out a branch that actually exists. This way of having several might be useful in projects with multiple repositories with different branch naming conventions.
Project ID can be found out in Softagram (via browser) by looking at the URL and using the ID from the URL (bolded):