Update project/import/bitbucket.md doc

doc/user/project/import/bitbucket.md

@@ -31,11 +31,11 @@ to enable this if not already.
 ## How it works
 
 When issues/pull requests are being imported, the Bitbucket importer tries to find
-the Bitbucket author/assignee in GitLab's database using the Bitbucket ID. For this
-to work, the Bitbucket author/assignee should have signed in beforehand in GitLab
-and **associated their Bitbucket account**. If the user is not
-found in GitLab's database, the project creator (most of the times the current
-user that started the import process) is set as the author, but a reference on
+the Bitbucket author/assignee in GitLab's database using the Bitbucket `nickname`. For this
+to work, the Bitbucket author/assignee should have their `nickname` match their Bitbucket
+`username`, signed in beforehand in GitLab and **associated their Bitbucket account**.
+If the user is not found in GitLab's database, the project creator (most of the times the
+current user that started the import process) is set as the author, but a reference on
 the issue about the original Bitbucket author is kept.
 
 The importer will create any new namespaces (groups) if they don't exist or in