Document migration of members

migration.md

@@ -7,6 +7,8 @@ The migration instructions for each part of the website are shown below.
 
 ## Active members
 
+This is taken care of during member migration.
+
 ## Documents
 
 ## Education
@@ -17,6 +19,15 @@ The migration instructions for each part of the website are shown below.
 
 ## Members
 
+To migrate members, committees, boards, memberships of committees and boards,
+as well as introductionmentorships, execute `python manage.py migratemembers`.
+
+Unfortunately, not all the data is complete. Most notably, some begin-dates are
+missing. This will need to be fixed manually. These have been set to 1970,
+as start dates are not optional.
+
+This migration typically takes a few minutes.
+
 ## Newsletters
 
 ## Partners