extend README for csv-based batch migration

Author: kathrin-7978

README.md

@@ -82,7 +82,8 @@ Go to [Settings / Access Tokens](https://gitlab.com/-/profile/personal_access_to
 
 #### gitlab.projectID
 
-Leave it null for the first run of the script. Then the script will show you which projects there are. Can be either string or number.
+Leave it null for the first run of the script (leave csvImport.projectMapCsv empty either). Then the script will show you which projects there are. Can be either string or number.
+Leave it null if you want to import multiple projects via csv file (set `csvImport` instead).
 
 #### gitlab.listArchivedProjects
 
@@ -156,6 +157,23 @@ Maps the usernames from gitlab to github. If the assinee of the gitlab issue is
 
 When one renames the project while transfering so that the projects don't loose there links to the mentioned issues.
 
+### csvImport.projectMapCsv
+
+Optional name of CSV file (located in project root) containing multiple projects for migration. If set, it overrules `gitlab.projectId` and `github.repo`.
+CSV file must contain the following values: GitLab project ID, GitLab project path, GitHub project path, e.g. 213,gitlab_namespace/gitlab_projectname,github_namespace/github_projectname
+
+### csvImport.gitlabProjectIdColumn
+
+Column in CSV file containing GitLab project ID
+
+### csvImport.gitlabProjectPathColumn
+
+Column in CSV file containing GitLab path
+
+### csvImport.githubProjectPathColumn
+
+Column in CSV file containing GitHub path
+
 ### conversion
 
 #### conversion.useLowerCaseLabels